Zoom optical system and image taking apparatus using the same

ABSTRACT

A zoom optical system comprising, in order from an object side: a first lens unit having a negative refractive power; a second lens unit having a positive refractive power; and a third lens unit having a positive refractive power, a space between the lens units being changed to thereby perform zooming and focusing, wherein the first lens unit is constituted of a negative lens.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/445,299 filed on Jun. 2, 2006 now U.S. Pat. No. 7,502,172, whichclaims benefit under 35 U.S.C. §119 of Japanese Patent Application No.2005-174,882 filed on Jun. 15, 2005; No. 2005-327,514, filed on Nov. 11,2005; and No. 2006-082,886, filed on Mar. 24, 2006, the contents ofwhich are incorporated herein in their entirety by reference thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom optical system, and an imagetaking apparatus provided with such zoom optical system.

2. Description of the Related Art

There have been known various zoom optical systems including: a firstlens unit having a negative refractive power; a second lens unit havinga positive refractive power; and a third lens unit having a positiverefractive power. In the optical system having such lens arrangement,since the first lens unit has a negative refractive power, the system isadvantageous in reducing a diameter of the optical system while securingan appropriate angle of field in a wide-angle end. In addition, variousfour-unit types of zoom optical systems have also been known. As suchzoom optical systems, there are known systems described in JapanesePatent Application Laid-Open Nos. 2004-318,099, 2004-318,106, and2004-318,107.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a comparatively compact high-performancezoom optical system, and an image taking apparatus using this zoomoptical system.

In the present invention, a first type of zoom optical system comprises,in order from an object side: a first lens unit having a negativerefractive power; a second lens unit having a positive refractive power;and a third lens unit having a positive refractive power, the zoomoptical system changing a space between the lens units to therebyperform zooming and focusing, the first lens unit being constituted of abiconcave negative lens, the zoom optical system satisfies the followingcondition (1):−3.0<(r _(1GF) +r _(1GR))/(r _(1GF) −r _(1GR))<0.3  (1),wherein r_(1GF) denotes a paraxial radius of curvature of an object-sidesurface of the negative lens of the first lens unit, and r_(1GR) denotesa paraxial radius of curvature of an image-side surface of the negativelens of the first lens unit.

In the present invention, a second type of zoom optical system has, inorder from an object side: a first lens unit having a negativerefractive power; a second lens unit having a positive refractive power;and a third lens unit having a positive refractive power, the zoomoptical system changing a space between the lens units to therebyperform zooming and focusing, the first lens unit being constituted of anegative lens, the zoom optical system satisfies the following condition(4):−5.0<f _(1G) /f _(2G)<−1.3  (4),wherein f_(1G) denotes a focal length of the first lens unit, and f_(2G)denotes a focal length of the second lens unit.

In the present invention, a third type of zoom optical system has, inorder from an object side: a first lens unit having a negativerefractive power; a second lens unit having a positive refractive power;and a third lens unit having a positive refractive power, the zoomoptical system changing a space between the lens units to therebyperform zooming and focusing, the first lens unit being constituted of anegative lens, the zoom optical system satisfying the followingconditions (5) to (7):1.8<f _(t) /f _(W)  (5);0.50<f _(2G) /f _(W)<2.00  (6); and1.0<d _(12W) /d _(23W)<∞  (7),wherein f_(W) denotes a focal length of the zoom optical system in awide-angle end, f_(t) denotes a focal length of the zoom optical systemin a telephoto end, f_(2G) denotes a focal length of the second lensunit, d_(12W) denotes an axial length between a lens surface of thefirst lens unit closest to an image side and a lens surface of thesecond lens unit closest to the object side in the wide-angle end, andd_(23W) denotes an axial length between a lens surface of the secondlens unit closest to the image side and a lens surface of the third lensunit closest to the object side in the wide-angle end.

In the present invention, a fourth type of zoom optical system has, inorder from an object side: a first lens unit having a negativerefractive power; a second lens unit having a positive refractive power;and a third lens unit having a positive refractive power, the zoomoptical system changing a space between the lens units to therebyperform zooming and focusing,

the first lens unit being constituted of a negative lens,

the second lens unit being constituted of, in order from the objectside, a positive lens, a positive lens directing a convex surface on theobject side and a negative lens directing a concave surface on an imageside, the positive lens directing a convex surface on the object sidebeing cemented to the negative lens directing a concave surface on theimage side.

In the present invention, a fifth type of zoom optical system has, inorder from an object side: a first lens unit having a negativerefractive power; a second lens unit having a positive refractive power;and a third lens unit having a positive refractive power, the zoomoptical system changing a space between the lens units to therebyperform zooming and focusing,

the first lens unit including one negative lens,

the third lens unit including a positive lens directing a convex surfaceon an image side,

the zoom optical system satisfying the following condition (8):0.1<(r _(3GF) +r _(3GR))/(r _(3GF) −r _(3GR))<5.0  (8),wherein r_(3GF) denotes a paraxial radius of curvature of an object-sidesurface of the positive lens of the third lens unit, and r_(3GR) denotesa paraxial radius of curvature of an image-side surface of the positivelens of the third lens unit.

In the present invention, a sixth type of zoom optical system has, inorder from an object side: a first lens unit having a negativerefractive power; a second lens unit having a positive refractive power;a third lens unit having a positive refractive power; and a fourth lensunit, the zoom optical system changing a space between the lens units tothereby perform zooming and focusing,

the first lens unit including a negative lens, the number of lensesincluded in the first lens unit being one,

the number of lenses included in the second lens unit being three,

the number of lenses included in the third lens unit being one,

the number of lenses included in the fourth lens unit being one,

the second lens unit including two positive lenses and a negative lens.

In the present invention, a seventh type of zoom optical system has, inorder from an object side: a first lens unit having a negativerefractive power; a second lens unit having a positive refractive power;a third lens unit having a positive refractive power; and a fourth lensunit, the zoom optical system changing a space between the lens units tothereby perform zooming and focusing, the fourth lens unit being fixedto an image surface.

In the present invention, an eighth type of zoom optical system has, inorder from an object side: a first lens unit having a negativerefractive power; a second lens unit having a positive refractive power;a third lens unit having a positive refractive power; and a fourth lensunit, the zoom optical system changing a space between the lens units tothereby perform zooming and focusing,

the first lens unit being constituted of a biconcave lens,

the second lens unit having an aperture stop,

the third lens unit being constituted of a positive lens having a convexsurface on an image side,

the fourth lens unit being constituted of a lens,

the number of the lenses constituting the second lens unit being notless than that of the lenses constituting the first lens unit, the thirdlens unit and the fourth lens unit.

In the present invention, an image taking apparatus comprises: the zoomoptical system of the present invention; and an image sensor disposed onan image-surface side of the zoom optical system.

Advantages of the invention will be set forth in the description whichfollows, and in part will be obvious from the description. Advantages ofthe invention may be realized and obtained by means of theinstrumentalities and combinations particularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given below and the accompanying drawings, whichare given by way of illustration only and thus are not limitative of thepresent invention, wherein:

FIGS. 1A to 1C are sectional views in an wide-angle end, an intermediatestate and a telephoto end of the zoom optical system of Example 1 of thepresent invention when focused on an infinite object;

FIGS. 2A to 2C are sectional views similar to those of FIG. 1 of Example2 of the present invention;

FIGS. 3A to 3C are sectional views similar to those of FIG. 1 of Example3 of the present invention;

FIGS. 4A to 4C are sectional views similar to those of FIG. 1 of Example4 of the present invention;

FIGS. 5A to 5C are sectional views similar to those of FIG. 1 of Example5 of the present invention;

FIGS. 6A to 6C are sectional views similar to those of FIG. 1 of Example6 of the present invention;

FIGS. 7A to 7C are sectional views similar to those of FIG. 1 of Example7 of the present invention;

FIGS. 8A to 8C are sectional views similar to those of FIG. 1 of Example8 of the present invention;

FIGS. 9A to 9C are sectional views similar to those of FIG. 1 of Example9 of the present invention;

FIGS. 10A to 10C are sectional views similar to those of FIG. 1 ofExample 10 of the present invention;

FIGS. 11A to 11C are sectional views similar to those of FIG. 1 ofExample 11 of the present invention;

FIGS. 12A to 12C are sectional views similar to those of FIG. 1 ofExample 12 of the present invention;

FIGS. 13A to 13C are sectional views similar to those of FIG. 1 ofExample 13 of the present invention;

FIGS. 14A to 14C are sectional views similar to those of FIG. 1 ofExample 14 of the present invention;

FIGS. 15A to 15C are sectional views similar to those of FIG. 1 ofExample 15 of the present invention;

FIGS. 16A to 16C are sectional views similar to those of FIG. 1 ofExample 16 of the present invention;

FIGS. 17A to 17C are sectional views similar to those of FIG. 1 ofExample 17 of the present invention;

FIGS. 18A to 18C are sectional views similar to those of FIG. 1 ofExample 18 of the present invention;

FIGS. 19A to 19C are aberration diagrams of Example 1 when focused onthe infinite object;

FIGS. 20A to 20C are aberration diagrams of Example 2 when focused onthe infinite object;

FIGS. 21A to 21C are aberration diagrams of Example 3 when focused onthe infinite object;

FIGS. 22A to 22C are aberration diagrams of Example 4 when focused onthe infinite object;

FIGS. 23A to 23C are aberration diagrams of Example 5 when focused onthe infinite object;

FIGS. 24A to 24C are aberration diagrams of Example 6 when focused onthe infinite object;

FIGS. 25A to 25C are aberration diagrams of Example 7 when focused onthe infinite object;

FIGS. 26A to 26C are aberration diagrams of Example 8 when focused onthe infinite object;

FIGS. 27A to 27C are aberration diagrams of Example 9 when focused onthe infinite object;

FIGS. 28A to 28C are aberration diagrams of Example 10 when focused onthe infinite object;

FIGS. 29A to 29C are aberration diagrams of Example 11 when focused onthe infinite object;

FIGS. 30A to 30C are aberration diagrams of Example 12 when focused onthe infinite object;

FIGS. 31A to 31C are aberration diagrams of Example 13 when focused onthe infinite object;

FIGS. 32A to 32C are aberration diagrams of Example 14 when focused onthe infinite object;

FIGS. 33A to 33C are aberration diagrams of Example 15 when focused onthe infinite object;

FIGS. 34A to 34C are aberration diagrams of Example 16 when focused onthe infinite object;

FIGS. 35A to 35C are aberration diagrams of Example 17 when focused onthe infinite object;

FIGS. 36A to 36C are aberration diagrams of Example 18 when focused onthe infinite object;

FIG. 37 is a front perspective view showing an appearance of a digitalcamera in which the zoom optical system of the present invention isincorporated;

FIG. 38 is a rear view of the digital camera of FIG. 37;

FIG. 39 is a diagrammatically sectional plan view of the digital cameraof FIG. 37 for explaining the internal constitution thereof;

FIG. 40 is a front perspective view of a personal computer whose coveris opened and in which the zoom optical system of the present inventionis incorporated;

FIG. 41 is a sectional view of an objective optical system of thepersonal computer;

FIG. 42 is a side view showing a state of FIG. 40;

FIG. 43 is a front view of a cellular phone in which the zoom opticalsystem of the present invention is incorporated;

FIG. 44 is a side view of the cellular phone shown in FIG. 43;

FIG. 45 is a sectional view of a image forming optical system of thecellular phone shown in FIG. 43; and

FIG. 46 is an explanatory view of an effective image taking region of animage sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

First, there will be described a basic constitution of a zoom opticalsystem of the present invention.

In the present invention, a zoom optical system is based on an opticalsystem having, in order from an object side: a first lens unit having anegative refractive power; a second lens unit having a positiverefractive power; and a third lens unit having a positive refractivepower. The optical system changes a space between the lens units tothereby perform zooming and focusing, and the first lens unit isconstituted of a negative lens.

That is, in the present invention, the zoom optical system is anegative-lead type zoom lens system which includes three or more lensunits, in order from an object side, of a negative lens unit, a positivelens unit and a positive lens unit.

According to such lens arrangement, even when a total length is reduced,an appropriate zooming ratio can be secured, and an angle of field in awide-angle end is easily secured.

On the other hand, when the angle of field is enlarged, the diameter ofthe first lens unit easily increases. Especially, when the number of thelenses in the first lens unit increases, the diameter of the lensdisposed on the object side easily increases.

Therefore, in the present invention, the first lens unit is constitutedof a negative lens. In consequence, the first lens unit is easilyminiaturized and thinned. This is advantageous in achieving a compactzoom optical system in use or in a collapsed state.

The above-described basic constitution is variously modified toconstitute each type of zoom optical system. Each type of optical systemwill be described hereinafter in detail.

The first type of zoom optical system comprises, in order from an objectside, a first lens unit having a negative refractive power, a secondlens unit having a positive refractive power and a third lens unithaving a positive refractive power. The zoom optical system changes aspace between the lens units to thereby perform zooming and focusing,the first lens unit is constituted of a biconcave negative lens, and thezoom optical system satisfies the following condition (1):−3.0<(r _(1GF) +r _(1GR))/(r _(1GF) −r _(1GR))<0.3  (1),wherein r_(1GF) denotes a paraxial radius of curvature of an object-sidesurface of the negative lens of the first lens unit, and r_(1GR) denotesa paraxial radius of curvature of an image-side surface of the negativelens of the first lens unit.

The condition (1) is set for satisfactorily performing miniaturizationand attaining an aberration balance in the state in which the zoomoptical system is used.

Below the lower limit of −3.0 in the condition (1), there increases anabsolute value of the curvature of the concave surface of the negativelens on the incidence side, and it becomes difficult to suppressdistortion and astigmatism on the wide-angle side.

On the other hand, above the upper limit of 0.3 in the condition (1),the principal point of the first lens unit comes close to the imageside, and this is disadvantageous in reducing a total length in theimage taking state. In addition, there decreases the absolute value ofthe curvature of the concave surface on the object side. This easilydegrades the spherical aberration correcting function of the first lens(the negative lens of the first lens unit), that is, the function ofintentionally generating a positive spherical aberration in the firstlens so that this positive spherical aberration cancels the sphericalaberration of the whole zoom lens.

In the first type, the negative lens of the first lens unit can beprovided with an aspherical surface having such a shape that thenegative refractive power of the surface weakens with distance from theoptical axis.

When the first lens unit is constituted of a negative lens, in the firstlens unit, a ray having a large incidence height easily has a largeincidence angle on a lens surface. The above-described constitutioninhibits the incidence angle of the ray having a large incidence heightfrom being excessively enlarged, and generations of miscellaneousaberrations are easily suppressed. Therefore, a satisfactory aperturecan be easily secured, and an optical performance can be appropriatelybalanced.

The aspherical surface can be disposed on the object-side surface of thenegative lens of the first lens unit.

Such constitution can reduce a protruding amount of the peripheralportion of the object-side concave surface of the negative lens, andthis is advantageous in reducing the total length.

The aspherical surface preferably satisfies the following condition (2):−0.1<Asp _(1GF) /r _(1GF)<0  (2),wherein Asp_(1GF) denotes a deviation of the aspherical surface from areference sphere in a position where an off-axial chief ray having amaximum angle of field passes through the object-side surface of thenegative lens of the first lens unit in the wide-angle end.

Especially, in a case where the aspherical surface is disposed on theobject side of the negative lens, the condition (2) is preferablysatisfied. It is to be noted that the deviation of the asphericalsurface is a length from a reference sphere (a spherical surface whosevertex comes into contact with the aspherical surface and which has aradius of curvature equal to a paraxial radius of curvature of theaspherical surface) to the aspherical surface, the length being measuredin a direction parallel to the optical axis.

Below the lower limit value of −0.1 in the condition (2), the deviationof the aspherical surface becomes excessively large, and an off-axialaberration tends to be overcorrected. On the other hand, above the upperlimit value of 0, the deviation of the aspherical surface becomesexcessively small, and the off-axial aberration tends to beundercorrected. The incident ray height tends to be large on awide-angle side, and an effect of miniaturization is weakened.

On the other hand, when the image-side surface of the negative lens ofthe first lens unit is formed to be aspherical, the off-axial aberrationof the first lens is effectively reduced.

In this case, the aspherical surface preferably satisfies the followingcondition (3):−0.01<Asp _(1GR) /r _(1GR)<0.1  (3),wherein Asp_(1GR) denotes a deviation of the aspherical surface from areference sphere in a position where the off-axial chief ray having amaximum angle of field passes through the image-side surface of thenegative lens of the first lens unit in the wide-angle end.

In a case where the condition (3) is satisfied, when surface shapes ofthe object-side surface and the image-side surface are adjusted, both ofthe correction of the off-axial aberration in the wide-angle end and theminiaturization can satisfactorily be realized.

Next, the second type of zoom optical system will be described. The zoomoptical system comprises, in order from an object side: a first lensunit having a negative refractive power; a second lens unit having apositive refractive power; and a third lens unit having a positiverefractive power. The zoom optical system changes a space between thelens units to thereby perform zooming and focusing, the first lens unitis constituted of a negative lens, and the zoom optical system satisfiesthe following condition (4):−5.0<f _(1G) /f _(2G)<−1.3  (4),wherein f_(1G) denotes a focal length of the first lens unit, and f_(2G)denotes a focal length of the second lens unit.

The condition (4) is set for satisfactorily miniaturizing the zoomoptical system and balancing aberrations in the state in which thesystem is used.

When the first lens unit is constituted of a negative lens, the lensunit advantageously becomes compact when collapsed.

On the other hand, when the first lens unit is constituted of a negativelens, an influence of the aberration on the first lens unit needs to beconsidered.

The second type of zoom optical system is constituted so that the abovecondition (4) is satisfied, and the first lens unit has an appropriatelysmall negative refractive power with respect to the positive refractivepower of the second lens unit. Therefore, even when the first lens unitis constituted of a negative lens, it is possible to suppress thegenerations of the aberrations in the first lens unit.

When the negative refractive power of the first lens unit is below thelower limit of −5.0 in the condition (4), the generation of theaberration in the first lens unit is easily suppressed. However, thespace between the first lens unit and the second lens unit needs to belengthened for the zooming, and the total length or diameter tends toincrease. Alternatively, the refractive power of the second lens unitbecomes excessively large, and the aberration of the second lens unit isnot easily suppressed. To avoid this, the number of the lensesconstituting the second lens unit needs to be increased, and it becomesdifficult to miniaturize the lens unit when collapsed.

On the other hand, when the negative refractive power of the first lensunit is above the upper limit of −1.3 in the condition (4), a largeoff-axial aberration is easily generated in the first lens unit, and itbecomes difficult to correct the aberration.

The negative lens of the first lens unit can be constituted as abiconcave negative lens.

Such constitution more preferably balances a compact size andmiscellaneous aberrations in the use state.

The negative lens preferably satisfies the following condition (1):−3.0<(r _(1GF) +r _(1GR))/(r _(1GF) −r _(1GR))<0.3  (1),wherein r_(1GF) denotes a paraxial radius of curvature of an object-sidesurface of the negative lens of the first lens unit, and r_(1GR) denotesa paraxial radius of curvature of an image-side surface of the negativelens of the first lens unit.

Such constitution is preferably advantageous in securing theminiaturization and an optical performance.

Moreover, it is more preferable that the object-side surface of thenegative lens is formed to be aspherical, and the following condition(2) is satisfied.−0.1<Asp _(1GF) /r _(1GF)<0  (2),wherein Asp_(1GF) denotes an deviation of the aspherical surface from areference sphere in a position where an off-axial chief ray having amaximum angle of field passes through the object-side surface of thenegative lens of the first lens unit in the wide-angle end.

Such constitution is more preferable in respect of aberration correctionand miniaturization.

The third type of zoom optical system comprises, in order from an objectside: a first lens unit having a negative refractive power; a secondlens unit having a positive refractive power; and a third lens unithaving a positive refractive power. The zoom optical system changes aspace between the lens units to thereby perform zooming and focusing,the first lens unit is constituted of a negative lens, and the zoomoptical system satisfies the following conditions (5) to (7):1.8<f _(t) /f _(W)  (5);0.50<f _(2G) /f _(W)<2.00  (6); and1.0<d _(12W) /d _(23W)<∞  (7),wherein f_(W) denotes a focal length of the zoom optical system in awide-angle end, f_(t) denotes a focal length of the zoom optical systemin a telephoto end, f_(2G) denotes a focal length of the second lensunit, d_(12W) denotes an axial length between a lens surface of thefirst lens unit closest to an image side and a lens surface of thesecond lens unit closest to the object side in the wide-angle end, andd_(23W) denotes an axial length between a lens surface of the secondlens unit closest to the image side and a lens surface of the third lensunit closest to the object side in the wide-angle end.

In the third type of zoom optical system, in a case where a necessaryray passes through the first lens unit in the vicinity of the wide-angleend in which the axial length between the first lens unit and the secondlens unit increases, an effective diameter of the first lens unit issubstantially determined.

Therefore, in the third type of zoom optical system, the focal length ofthe second lens unit is appropriately shortened so as to prevent thefirst lens unit from being too much separated from the second lens unitin the wide-angle end.

The condition (5) means a zooming ratio of the whole zoom opticalsystem, and is a prerequisite in defining the focal length of the secondlens unit.

The condition (6) defines the focal length of the second lens unit whichis normalized with that of the whole zoom optical system in thewide-angle end.

When the first lens unit is constituted of a negative lens, the totallength is reduced, and also it is possible to provide a margin in thechange of the space between the first lens unit and the second lensunit. On the other hand, when the negative refractive power of the firstlens unit is strengthened, it becomes difficult to correct theaberration generated in the first lens unit.

However, when an appropriately strong refractive power is imparted tothe second lens unit as defined in the condition (6), the zooming ratioabove 1.8 is advantageously secured.

When the condition (6) is below the lower limit of 0.50, and therefractive power of the second lens unit increases, this isdisadvantageous for the aberration correction of the second lens unit.

When the condition (6) is above the upper limit of 2.00, and therefractive power of the second lens unit decreases, the change of thespace between the first lens unit and the second lens unit increases soas to secure the zooming ratio, and an effect of miniaturization isweakened. Alternatively, to realize both of the securing of the zoomingratio and the miniaturizing, the refractive power of the first lens unithas to be strengthened. Therefore, the constituting the first lens unitof a negative lens is disadvantageous in inhibiting the generation ofthe aberration in the first lens unit.

The condition (7) defines the axial length between the first lens unitand the second lens unit with respect to the axial length between thesecond lens unit and the third lens unit in the wide-angle end.

If the condition (7) is below the lower limit of 1.0, this isdisadvantageous in securing the refractive power of the second lens unitand securing the space between the first lens unit and the second lensunit. This is also disadvantageous in securing both of theminiaturization and the zooming ratio. Alternatively, the refractivepowers of the first and second lens units tend to be strengthened, andit becomes difficult to balance the aberrations in the whole zoomingrange.

The second lens unit can be constituted of three lenses including twopositive lenses and one negative lens.

When the first lens unit is constituted of a negative lens, it isdifficult to impart a strong refractive power to the first lens unit,and the positive refractive power is concentrated on the second lensunit. Therefore, it is preferable that the aberrations of the secondlens unit itself are reduced.

The second lens unit includes two positive lenses, and the positiverefractive power is shared by these two positive lenses so as to easilyinhibit the generation of the aberration. Furthermore, one negative lensis disposed to generate an aberration opposite to that of the positivelens, and the generation of the spherical aberration or the like can beinhibited in the second lens unit.

Next, the fourth type of zoom optical system will be described. The zoomoptical system comprises, in order from an object side: a first lensunit having a negative refractive power; a second lens unit having apositive refractive power; and a third lens unit having a positiverefractive power. The zoom optical system changes a space between thelens units to thereby perform zooming and focusing, and the first lensunit is constituted of a negative lens.

The second lens unit is constituted of, in order from the object side, apositive lens, a positive lens directing its convex surface on theobject side and a negative lens directing its concave surface on animage side, the positive lens directing its convex surface on the objectside being cemented to the negative lens directing its concave surfaceon the image side.

In the fourth type of zoom optical system, when the first lens unit isconstituted of a negative lens, a burden of the zooming function imposedon the second lens unit increases. To solve this problem, the secondlens unit is constituted of, in order from the object side, the positivelens, the positive lens directing its convex surface on the object sideand the negative lens directing its concave surface on the image side,and the positive refractive power is shared by two positive lenses.Moreover, the spherical aberration opposite to that of the positive lensis generated in the negative lens, so that the optical performancebecomes satisfactory.

Moreover, in the second lens unit, the positive lens is cemented to thenegative lens to thereby reduce influences of eccentricities of thepositive and negative lenses. This is also advantageous in obtaining acompact zoom optical system in the collapsed state.

Furthermore, when the lenses are arranged as described above, theprincipal point of the second lens unit can be brought close to anobject, and this is advantageous in miniaturization of the zoom opticalsystem and enhancement of the zooming ratio.

In the fourth type of zoom optical system, an aperture stop can bedisposed between the positive lens and the positive lens directing itsconvex surface on the object side in the second lens unit.

When the first lens unit is constituted of only one negative lens, theaperture stop is preferably disposed in the above-described position. Bydisposing the aperture stop in this position, the negative lens and thepositive lens are arranged on the object side of the aperture stop. Thisis advantageous in correcting distortion or chromatic aberration ofmagnification. This is also advantageous in that the aperture stop isnot excessively separated from the first lens unit, and the diameter ofthe first lens unit is reduced.

The aperture shape of the aperture stop may be fixed. In this case, amember for adjusting brightness may be disposed in a space between otherlenses.

In this constitution, since the aperture shape of the aperture stop isfixed, the lenses before and after the aperture stop can be broughtclose to the aperture stop, and this is advantageous in achieving acompact zoom optical system. It is especially preferable that thebrightness adjusting member is constituted as a stop having a variableaperture shape, the member is disposed immediately before the secondlens unit, and the member is constituted so as to move integrally withthe second lens unit during the zooming.

According to such constitution, the diameters of the lens units are wellbalanced in a state having a small F number. In addition, since a chiefray position deviates little during the brightness adjustment, thesystem can be constituted with less aberration fluctuations.

Next, the fifth type of zoom optical system will be described. The zoomoptical system comprises, in order from an object side: a first lensunit having a negative refractive power; a second lens unit having apositive refractive power; and a third lens unit having a positiverefractive power. The zoom optical system changes a space between thelens units to thereby perform zooming and focusing, the first lens unitis constituted of a negative lens, the third lens unit includes apositive lens directing its convex surface on an image side, and thezoom optical system satisfies the following condition (8):0.1<(r _(3GF) +r _(3GR))/(r _(3GF) −r _(3GR))<5.0  (8),wherein r_(3GF) denotes a paraxial radius of curvature of an object-sidesurface of the positive lens of the third lens unit, and r_(3GR) denotesa paraxial radius of curvature of an image-side surface of the positivelens of the third lens unit.

The constituting the third lens unit of a positive lens is advantageousin securing the movement space of the second lens unit, achievingminiaturization, and increasing the zooming ratio. The third lens unitis formed into such a shape that the above condition (8) is satisfied,and the curvature of the convex image-side surface of the positive lensis increased. Accordingly, while the principal point is brought close tothe image side, and aberrations are balanced, the positive lens isbrought close to the center of the optical system (as viewed in theoptical axis direction), and the diameter of the lens is inhibited frombeing enlarged.

If the condition (8) is below the lower limit of 0.1, an incidence angleof an off-axial ray increases in the object-side surface of the thirdlens unit. This is disadvantageous in correcting an off-axialaberration. If the condition (8) is above the upper limit of 5.0, thethird lens unit has an extreme meniscus shape, and it becomes difficultto inhibit the generation of the aberration in the image-side surface.

In the fifth type, the focusing may be performed by moving only thethird lens unit.

According to such constitution, since only one lens is movable duringthe focusing, a driving mechanism for the focusing can be simplified.Especially, since the third lens unit has a convex surface having alarge curvature on the image side, there are reduced fluctuations of theincidence angle of an off-axial chief ray due to the movement for thefocusing. There are also reduced aberration fluctuations due to themovement of the third lens unit for the focusing.

Moreover, when the third lens unit is constituted of a plastic moldedlens, the lens can be inexpensive.

Furthermore, the image-side surface of the third lens unit has a largecurvature, but when this surface is formed to be aspherical, thegenerations of the aberrations can be easily inhibited.

It is to be noted that each type of zoom optical system can beconstituted so that a fourth lens unit having an aspherical surface isdisposed between the third lens unit and the image surface, and thespace between the third lens unit and the fourth lens unit is changedfor the zooming or the focusing.

When the fourth lens unit is disposed between the third lens unit andthe image surface, and the aspherical surface is disposed in the fourthlens unit, it is easy to obtain a function of maintaining flatness ofthe image surface at a time when the space between the third lens unitand the fourth lens unit is changed, or adjusting fluctuations of theentrance pupil position.

Moreover, this type of zoom optical system has an effect of reducing theaberration fluctuations in a case where the focusing is performed bymoving only the third lens unit.

Furthermore, when any lens having the aspherical surface in the fourthlens unit is the plastic molded lens, the lens becomes light in weightand it becomes easy to manufacture the aspherical surface.

In addition, each type of zoom optical system can be constituted so thatthe fourth lens unit as a single lens is disposed between the third lensunit and the image surface, and the space between the third lens unitand the fourth lens unit is changed for the zooming or the focusing.

Such constitution is preferable in reducing the total length of the zoomoptical system.

Moreover, each type of zoom optical system can be constituted so thatthe fourth lens unit having a positive refractive power is disposedbetween the third lens unit and the image surface, and the space betweenthe third lens unit and the fourth lens unit is changed for the zoomingor the focusing.

Such constitution is preferable in correcting the aberration, becausethe positive refractive power of the fourth lens unit can share a partof the positive refractive power of the third lens unit.

Furthermore, in the constitution in which the space between the thirdlens unit and the fourth lens unit is changed for the zooming, an effectis easily obtained such as reduction of aberration fluctuationsaccompanying the zooming, reduction of fluctuations of the entrancepupil position or reduction of fluctuations of the total length.

In addition, fixing of the fourth lens unit during the zooming and thefocusing is advantageous in miniaturizing the lens driving mechanism.

Moreover, it is preferable that the change amount of the space betweenthe third lens unit and the fourth lens unit during the zooming is smallas compared with the change amount of the space between the first lensunit and the second lens unit and the change amount of the space betweenthe second lens unit and the third lens unit. According to suchconstitution, the aberration fluctuations accompanying the movement ofthe third lens unit can be reduced.

Next, the sixth type of zoom optical system will be described. The zoomoptical system comprises, in order from an object side: a first lensunit having a negative refractive power; a second lens unit having apositive refractive power; a third lens unit having a positiverefractive power; and a fourth lens unit, and the zoom optical systemchanges a space between the lens units to thereby perform zooming andfocusing. The first lens unit includes a negative lens, the number oflenses included in the first lens unit is one, the number of lensesincluded in the second lens unit is three, the number of lenses includedin the third lens unit is one, the number of lenses included in thefourth lens unit is one, and the second lens unit is constituted of twopositive lenses and a negative lens.

Such constitution is advantageous in maintaining an aberrationperformance while constituting the optical system to be compact in aused or collapsed state.

To miniaturize the zoom optical system in the used or collapsed state,it is advantageous to reduce the number of the tenses included in thezoom optical system. In the case where the zoom optical systemcomprises, in order from the object side, four or more lens units of anegative lens unit, a positive lens unit, a positive lens unit and alens unit, the height of the off-axial ray is large in the first lensunit. Therefore, the first lens unit constituted of one lens isadvantageous in reducing the size of the zoom optical system in thediametric direction. In the first lens unit constituted of one negativelens, enlargement of the first lens unit in a thickness direction iseasily inhibited. This is advantageous in reducing the total length inthe used or collapsed state.

On the other hand, the second lens unit having the positive refractivepower has a function of performing the zooming by changing the spacebetween the first lens unit and the second lens unit. Therefore, theburden of the zooming function imposed on the second lens unit easilybecomes large, and influences on aberration fluctuations easily becomelarge. Therefore, when the three lenses in the second lens unit includetwo positive lenses and one negative lens, the positive refractive powerof the second lens unit is easily secured. Moreover, since one negativelens is included in the second lens unit, aberrations of the second lensunit itself are easily reduced.

Moreover, since the second lens unit performs a zooming function or thelike, each of the third lens unit and the fourth lens unit may beconstituted of one lens, and this contributes to miniaturization.

It is to be noted that in a case where a lens unit is further providedin addition to the first lens unit having the negative refractive power,the second lens unit having the positive refractive power and the thirdlens unit having the positive refractive power arranged in order fromthe object side, it is preferable that the fourth lens unit is addedbetween the third lens unit and the image, and the zoom optical systemis formed as a four-unit zoom optical system as a whole.

Such constitution is preferable for miniaturizing the zoom opticalsystem and maintaining the optical performance.

In a case where the fourth lens unit is added, the fourth lens unit ispreferably fixed during the zooming. Such constitution is preferable,because a movement mechanism for the zooming can be simplified.

In each type of zoom optical system described above, the total number ofthe lenses included in the zoom optical system is preferably six. Suchconstitution is more preferable in constituting the system to becompact.

Moreover, each type of zoom optical system described above preferablysatisfies the following condition:0.6<TLG _(sum) /f _(W)<1.7  (9),wherein TLG_(sum) denotes a sum of thicknesses of the lens unitsconstituting the zoom optical system, and f_(W) denotes a focal lengthof the zoom optical system in the wide-angle end.

If the condition (9) is below the lower limit of 0.6, the thickness ofthe lens unit is reduced, and it becomes difficult to miniaturize thesystem while the aberrations are kept in balance. If the condition (9)is above the upper limit of 1.7, the thickness of the zoom opticalsystem, when collapsed, increases.

Instead of the condition (9), the following condition (10) or (11) maybe satisfied. Moreover, these conditions may be satisfied at the sametime:0.2<TLG _(sum) /f _(t)<1.5  (10),wherein TLG_(sum) denotes the sum of the thicknesses of the lens unitsconstituting the zoom optical system, and f_(t) denotes a focal lengthof the zoom optical system in a telephoto end.

If the condition (10) is below the lower limit of 0.2, the thickness ofthe lens unit is reduced, and it becomes difficult to miniaturize thesystem while the aberrations are kept in balance. If the condition (10)is above the upper limit of 1.5, the thickness of the zoom opticalsystem, when collapsed, increases.1.2<TLG _(sum) /Y′<3.0  (11),wherein TLG_(sum) denotes the sum of the thicknesses of the lens unitsconstituting the zoom optical system, and Y′ denotes an image height. Inthe case where the zoom optical system is used with an electronic imagesensor, the image height Y′ is a half of the diagonal length of aneffective image taking region of the light receiving surface of theimage sensor.

If the condition (11) is below the lower limit of 1.2, the thickness ofthe lens unit is reduced, and it becomes difficult to miniaturize thesystem while the aberrations are kept in balance. If the condition (11)is above the upper limit of 3.0, the thickness of the zoom opticalsystem, when collapsed, increases.

It is to be noted that the effective image taking region of the lightreceiving surface means a region for obtaining image information for usein printing, displaying or the like on the light receiving surface ofthe image sensor which receives an optical image formed by the zoomoptical system.

In a case where the effective image taking region of the image sensor isrectangular, and the optical axis of the zoom lens system passes throughthe center of the effective image taking region, the image height in theeffective image taking region of the light receiving surface is a halfof the diagonal length L of the effective image taking region. Thediagonal length L of the effective image taking region will bedescribed. FIG. 46 is a diagram showing an example of the pixelarrangement on the image receiving surface of the image sensor. In thisexample, red (R), green (G) and blue (B) pixels are arranged at an equalpitch in a mosaic form. The effective image taking region means a regionin the light receiving surface of the image sensor for use inreproducing the taken image (displaying the image in a personalcomputer, printing the image by a printer or the like).

An effective image taking region EI is sometimes set to be smaller thanthe whole light receiving surface of the image sensor in accordance witha performance of the optical system as shown in, for example, FIG. 46.For example, as to an image (image circle) obtained by the opticalsystem, an image quality of a peripheral portion is inferior to that ofthe center in many cases. In such case, it is an example that the regionis set to be small, in which a part of the peripheral portion of theimage circle is not used in reproducing the image. In this example, thelength L is the diagonal length of this effective image taking regionset to be small.

Each type of zoom optical system described above preferably satisfiesthe following condition (12):−3.0<Δ_(12WT) /f _(W)<−1  (12),wherein Δ_(12WT) denotes a difference of a space between the first lensunit and the second lens unit in the telephoto from that in thewide-angle end, and f_(W) denotes a focal length of the zoom opticalsystem in the wide-angle end.

If the condition (12) is below the lower limit value of −3.0, the totallength easily increases. If the condition (12) exceeds the upper limitvalue of −1, the zoom optical system is disadvantageous in securing azooming ratio.

Instead of the condition (12), the following condition (13) or (14) maybe satisfied. Moreover, these condition formulas may be satisfied at thesame time:−0.9<Δ_(12WT) /f _(t)<−0.3  (13),wherein Δ_(12WT) denotes a difference of a space between the first lensunits and the second lens units in the telephoto end from that in thewide-angle end, and f_(t) denotes a focal length of the zoom opticalsystem in the telephoto end.−5.0<Δ_(12WT) /Y′<−1.0  (14),wherein Δ_(12WT) denotes a difference of a space between the first lensunits and the second lens units in the telephoto end and the wide-angleend. In the case where the zoom optical system is used with anelectronic image sensor, the image height Y′ is a half of the diagonallength of an effective image taking region of the light receivingsurface of the image sensor.

Next, a seventh type of zoom optical system will be described. The zoomoptical system comprises, in order from an object side: a first lensunit having a negative refractive power; a second lens unit having apositive refractive power; a third lens unit having a positiverefractive power; and a fourth lens unit, the zoom optical systemchanges a space between the lens units to thereby perform zooming andfocusing, and the fourth lens unit is fixed to an image surface.

According to such constitution, it is possible to achieve a small-sizedzoom optical system which has less constituting lenses and whose zoomingratio is about three-fold.

In this type of zoom optical system, the focusing can be performed bymoving only the third lens unit.

Moreover, each of the first lens unit and the fourth lens unit ispreferably constituted of one lens element. Furthermore, the third lensunit is preferably constituted of one lens element.

In addition, the fourth lens unit preferably has the positive refractivepower.

Moreover, the first lens unit preferably moves along a locus convextoward the image side during the zooming from the wide-angle end towardthe telephoto end.

Furthermore, the second lens unit preferably moves toward the objectside during the zooming from the wide-angle end toward the telephotoend.

In addition, preferably, the movement amount of the third lens unit,during the zooming from the wide-angle end to the telephoto end whenfocused on an infinite object, is smaller than the movement amount of afocusing lens unit during focusing from an object at infinity to anobject at the minimum object distance in the telephoto end.

Moreover, the second lens unit is preferably constituted of a positivelens element and a negative lens component. Here, the lens componentmeans a single lens or a cemented lens.

Furthermore, the second lens unit is preferably constituted of, in orderfrom the object side, a positive lens element, and a cemented lensformed by cementing a positive lens element to a negative lens element.

In addition, an aperture stop is preferably disposed between thepositive lens element and the negative lens component in the second lensunit.

Moreover, a light quantity adjusting element is arranged with a lenscomponent between the aperture stop and the light quantity adjustingelement. Here, the light quantity adjusting element includes an elementsuch as a shutter for adjusting a quantity of light with an elapse oftime, and an element such as an ND filter for changing lighttransmittance to adjust the quantity of light.

Furthermore, the zoom optical system is preferably constituted so thatthe maximum ray height of the fourth lens unit is higher than that ofthe third lens unit in a wide-angle state, and the maximum ray height ofthe fourth lens unit is lower than that of the third lens unit in atelephoto state.

Next, the eighth type of zoom optical system will be described. The zoomoptical system comprises, in order from an object side: a first lensunit having a negative refractive power; a second lens unit having apositive refractive power; a third lens unit having a positiverefractive power; and a fourth lens unit, and the zoom system changes aspace between the lens units to thereby perform zooming and focusing.

The first lens unit is constituted of a biconcave lens, the second lensunit has an aperture stop, the third lens unit is constituted of apositive lens having a convex surface on an image side and the fourthlens unit is constituted of a lens.

The number of the lenses constituting the second lens unit is not lessthan that of the lenses constituting the first lens unit, the third lensunit and the fourth lens unit.

In the first lens unit, the outer diameter tends to increase in order tosecure the angle of field on the wide-angle side. This tendency isstrengthened, when the total length of the first lens unit increases.When the first lens unit is constituted of one lens, the number of theconstituting lenses is reduced. Therefore, the zoom optical system canbe constituted to be compact, and the outer diameter can be reduced.When this lens is constituted to be biconcave, basic (low-order)aberration correction can efficiently be performed in two surfaces. Onthe other hand, when the first lens unit is constituted of one lens, acapability of correcting a chromatic aberration becomes insufficient inthe first lens unit.

To effectively compensate for this insufficiency, the third lens unit isconstituted of one positive lens having a convex surface on an imageside. Since the convex surface is disposed on the image side, theprincipal point is moved toward an image side, and the correction effectcan be improved. Moreover, the exit pupil position can be shifted towardthe object side, and the position can be adapted to a characteristic ofan image sensor (the exit pupil comes close to a position forestablishing an image-side telecentric optical system). Furthermore, thefourth lens unit is disposed in order to reduce image surfacefluctuations generated by the third lens unit constituted of the lenshaving the convex surface on the image side. Each of the first lensunit, the third lens unit and the fourth lens unit is constituted of onelens. Moreover, since the second lens unit bears the burden ofaberration correcting function of various aberrations, mainly an axialaberration, the number of the lenses constituting the second lens unitis set to be not less than that of the lenses constituting the firstlens unit, the third lens unit and the fourth lens unit. In the secondlens unit, even if the number of the lenses increases, the lens outerdiameter can be reduced because the lens is disposed in the vicinity ofthe aperture stop. Therefore, it is possible to use the lens havingsmall lens thickness. Also, an eccentricity between the lenses can bereduced by assembling the lens unit with high precision. Therefore, thisis not contrary to the compactness.

The second lens unit is preferably constituted of four or less lensesincluding at least two positive lenses and at least one negative lens.This arrangement is suitable for strengthening the positive power of thesecond lens unit, and correcting the chromatic aberration. The secondlens unit is further preferably constituted of two positive lenses andone negative lens.

This type of zoom optical system can be constituted so that the fourthlens unit is constituted of a meniscus lens directing its concavesurface on the object side, and the third lens unit is moved to performfocusing.

A concave surface is disposed on the object side of the fourth lensunit. Therefore, even when the third lens unit is moved to perform thefocusing, especially fluctuations of a curvature of field can bereduced. Furthermore, when the fourth lens unit is constituted of ameniscus lens, the space occupied by the fourth lens unit can bereduced.

The fourth lens unit is further preferably fixed with respect to theimage surface during the zooming and the focusing.

Moreover, this type of zoom lens preferably satisfies the followingcondition (1):−3.0<(r _(1GF) +r _(1GR))/(r _(1GF) −r _(1GR))<0.3  (1),wherein r_(1GF) denotes a paraxial radius of curvature of an object-sidesurface of the negative lens of the first lens unit, and r_(1GR) denotesa paraxial radius of curvature of an image-side surface of the negativelens of the first lens unit.

Furthermore, this type of zoom optical system preferably satisfies thefollowing conditions (5) to (7):1.8<f _(t) /f _(W)  (5);0.50<f _(2G) /f _(W)<2.00  (6); and1.0<d _(12W) /d _(23W)<∞  (7),wherein f_(W) denotes a focal length of the zoom optical system in awide-angle end, f_(t) denotes a focal length of the zoom optical systemin a telephoto end, f_(2G) denotes a focal length of the second lensunit, d_(12W) denotes an axial length between a lens surface of thefirst lens unit closest to an image side and a lens surface of thesecond lens unit closest to the object side in the wide-angle end, andd_(23W) denotes an axial length between a lens surface of the secondlens unit closest to the image side and a lens surface of the third lensunit closest to the object side in the wide-angle end.

Moreover, this type of zoom optical system may be constituted so that anaperture shape of the aperture stop is fixed, and a member for adjustingbrightness is disposed in a space between other lenses.

Furthermore, this type of zoom optical system preferably satisfies thefollowing condition (8):0.1<(r _(3GF) +r _(3GR))/(r _(3GF) −r _(3GR))<5.0  (8),wherein r_(3GF) denotes a paraxial radius of curvature of an object-sidesurface of the positive lens of the third lens unit, and r_(3GR) denotesa paraxial radius of curvature of an image-side surface of the positivelens of the third lens unit.

The above constitutions can appropriately be combined regardless ofwhether the constitutions have been described above as modifications ofone type or as different types. Moreover, when a plurality ofconstitutions is simultaneously satisfied, a miniaturizing effect, anaberration correcting effect and the like can be obtained more easily.

That is, even when constitutions described in a certain type of zoomoptical system are applied to another type of zoom optical system, amore preferable effect can be obtained.

Moreover, the above-described conditions may arbitrarily be combined.

Furthermore, it is more preferable from a viewpoint of correction of anoff-axial aberration that in the condition (1), the lower limit value isset to −2.0, further −1.0. From a viewpoint of miniaturization orcorrection of an axial aberration, it is more preferable that the upperlimit value is set to 0.1, further 0.00, still further −0.005.

It is more preferable from a viewpoint of the aberration correction thatin the condition (2), the lower limit value is set to −0.08, further−0.05. It is more preferable that the upper limit value is set to −0.01.

It is more preferable from a viewpoint of the aberration correction thatin the condition (3), the lower limit value is set to 0.00, further0.0005. It is more preferable that the upper limit value is set to 0.05,further 0.01.

It is more preferable from a viewpoint of the correction of theoff-axial aberration that in the condition (4), the lower limit value isset to −3.0, further −2.0. From a viewpoint of the miniaturization orthe correction of the axial aberration, it is more preferable that theupper limit value is set to −1.4, further −1.5.

It is preferable that the upper limit value of the condition (5) is setto 20.0 so as to prevent the zooming ratio from being excessively large.In a case where the zooming ratio is excessively large, when themaintaining of the optical performance and the constituting of thecompact zoom optical system are to be achieved at the same time, thelens shape becomes complicated, or the number of necessary lensesincreases, or an optical material to be used becomes expensive.Furthermore, it is more preferable from viewpoints of an opticalperformance and miniaturization that the lower limit value is set to 2.5and the upper limit value is set to 4.0.

In addition, it is more preferable that the lower limit value of thecondition (6) is set to 1.0, further 1.2. It is more preferable that theupper limit value is set to 1.8, further 1.6.

It is more preferable that the lower limit value of the condition (7) isset to 2.0, further 4.0. When the upper limit value is set to 20.0, itbecomes easy to give the third lens unit a function of collimating theoff-axial light beams from the second lens unit. In a case where thethird lens unit is moved to perform the focusing, it is possible tosecure a space for the focusing movement in the wide-angle end.Furthermore, it is more preferable to set the upper limit value to 10.0.

Moreover, as to the condition (8), it is more preferable that the lowerlimit value is set to 0.3, further 0.5. It is more preferable that theupper limit value is set to 3.0, further 2.5.

Moreover, it is more preferable that the lower limit value of thecondition (9) is set to 0.8, further 1.0. It is more preferable to setthe upper limit value to 1.5, further 1.3.

Furthermore, it is more preferable that the lower limit value of thecondition (10) is set to 0.25, further 0.3. It is more preferable to setthe upper limit value to 0.45, further 0.43.

In addition, as to the condition (11), it is more preferable that thelower limit value is set to 1.5, further 1.8. It is more preferable thatthe upper limit value is set to 2.8, further 2.5.

Moreover, it is more preferable that the lower limit value of thecondition (12) is set to −2.5, further −2.2. The upper limit value ismore preferably set to −1.3, further −1.5.

Furthermore, as to the condition (13), it is more preferable that thelower limit value is set to −0.8, further −0.7. It is more preferablethat the upper limit value is set to −0.4, further −0.5.

Moreover, it is more preferable that the lower limit value of thecondition (14) is set to −4.0, further −3.5. The upper limit value ismore preferably set to −1.5, further −2.0.

Each of the above zoom optical systems has less constituting lenses, issmall-sized, and has a satisfactory performance. The constitution isadvantageous in miniaturizing the system when collapsed.

All of the above zoom optical systems can be used as an image takingoptical system of an image taking apparatus. The image taking apparatusof the present invention includes any of the above-described zoomoptical systems and an electronic image sensor disposed on the imageside of the zoom optical system.

Since the above zoom optical system is advantageous for theminiaturization, the image taking apparatus using this zoom opticalsystem is also advantageous for the miniaturization.

Next, specific numerical examples will be described.

Examples 1 to 18 of the zoom optical system will be describedhereinafter. FIGS. 1A to 18C show sectional views of the zoom opticalsystems of the Examples 1 to 18 when focused on an infinite object. Inthese drawings, FIGS. 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A, 9A, 10A, 11A, 12A,13A, 14A, 15A, 16A, 17A and 18A are sectional views in the wide-angleend. FIGS. 1B, 2B, 3B, 4B, 5B, 6B, 7B, 8B, 9B, 10B, 11B, 12B, 13B, 14B,15B, 16B, 17B and 18B are sectional views in an intermediate state.FIGS. 1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, 11C, 12C, 13C, 14C, 15C,16C, 17C and 18C are sectional views in the telephoto end. In thesedrawings: a first lens unit is denoted with G1; a second lens unit isdenoted with G2; a third lens unit is denoted with G3; a fourth lensunit is denoted with G4; an aperture stop is denoted with S; F denotes aparallel flat plate constituting a low pass filter coated with awavelength range restricting coating which cuts off an infrared light; Cdenotes a parallel flat plate which is a cover glass of an electronicimage sensor such as a CCD image sensor or a CMOS type image sensor; andan image surface is denoted with I. It is to be noted that the surfaceof the cover glass C may be coated with a wavelength range restrictingmulti-layer thin film. The cover glass C may be provided with a low passfilter function.

Example 1

As shown in FIGS. 1A to 1C, the zoom optical system of Example 1comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the image side in the telephotoend than in the wide-angle end. The aperture stop S and the second lensunit G2 integrally and monotonously move toward the object side. Thethird lens unit G3 moves along a locus concave toward the object sidewhile increasing the space between the third lens unit and the secondlens unit G2. The third lens unit is arranged slightly closer to theimage side in the telephoto end than in the wide-angle end. The fourthlens unit G4 is fixed with respect to the image surface I.

The first lens unit G1 is constituted of one biconcave negative lens,and the second lens unit G2 is constituted of, in order from the objectside, a biconvex positive lens, and a cemented lens of a biconvexpositive lens and a biconcave negative lens. The third lens unit G3constituted of one positive meniscus lens directing its concave surfaceon the object side, and the fourth lens unit G4 constituted of onepositive meniscus lens directing its concave surface on the object side.The aperture stop S is disposed between the biconvex positive lens andthe cemented lens of the biconvex positive lens and the biconcavenegative lens in the second lens unit G2.

Aspherical surfaces are used on six surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; opposite surfaces ofthe biconvex positive single lens of the second lens unit G2; theimage-side surface of the positive meniscus lens of the third lens unitG3; and the object-side surface of the positive meniscus lens of thefourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 2

As shown in FIGS. 2A to 2C, the zoom optical system of Example 2comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the image side in the telephotoend than in the wide-angle end. The aperture stop S and the second lensunit G2 integrally and monotonously move toward the object side. Thethird lens unit G3 moves along a locus concave toward the object sidewhile increasing the space between the third lens unit and the secondlens unit G2. The third lens unit is arranged slightly closer to theimage side in the telephoto end than in the wide-angle end. The fourthlens unit G4 is fixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, and a cemented lens of a biconvex positive lensand a biconcave negative lens. The third lens unit G3 constituted of onepositive meniscus lens directing its concave surface on the object side,and the fourth lens unit G4 constituted of one positive meniscus lensdirecting its convex surface on the object side. The aperture stop S isdisposed between the biconvex positive lens and the cemented lens of thebiconvex positive lens and the biconcave negative lens in the secondlens unit G2.

Aspherical surfaces are used on five surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface of the biconvex positive single lens of the second lens unit G2;the image-side surface of the positive meniscus lens of the third lensunit G3; and the object-side surface of the positive meniscus lens ofthe fourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.6 mm.

Example 3

As shown in FIGS. 3A to 3C, the zoom optical system of Example 3comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged closer to the image side in the telephoto end thanin the wide-angle end. The aperture stop S and the second lens unit G2integrally and monotonously move toward the object side. The third lensunit G3 slightly moves toward the image side while increasing the spacebetween the third lens unit and the second lens unit G2, and the fourthlens unit G4 is fixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, and a cemented lens of a biconvex positive lensand a biconcave negative lens. The third lens unit G3 constituted of onepositive meniscus lens directing its concave surface on the object side,and the fourth lens unit G4 constituted of one positive meniscus lensdirecting its convex surface on the object side. The aperture stop S isdisposed between the biconvex positive lens and the cemented lens of thebiconvex positive lens and the biconcave negative lens in the secondlens unit G2.

Aspherical surfaces are used on six surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface of the biconvex positive single lens of the second lens unit G2;the image-side surface of the positive meniscus lens of the third tensunit G3; and opposite surfaces of the fourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.6 mm.

Example 4

As shown in FIGS. 4A to 4C, the zoom optical system of Example 4comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged closer to the image side in the telephoto end thanin the wide-angle end. The aperture stop S and the second lens unit G2integrally and monotonously move toward the object side. The third lensunit G3 moves along a locus concave toward the object side whileincreasing the space between the third lens unit and the second lensunit G2, and is arranged slightly closer to the image side in thetelephoto end than in the wide-angle end. The fourth lens unit G4 isfixed with respect to an image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, and a cemented lens of a biconvex positive lensand a biconcave negative lens. The third lens unit G3 constituted of onepositive meniscus lens directing its concave surface on the object side,and the fourth lens unit G4 constituted of one positive meniscus lensdirecting its convex surface on the object side. The aperture stop S isdisposed between the biconvex positive lens and the cemented lens of thebiconvex positive lens and the biconcave negative lens in the secondlens unit G2.

Aspherical surfaces are used on six surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface of the biconvex positive single lens of the second lens unit G2;the image-side surface of the positive meniscus lens of the third lensunit G3; and opposite surfaces of the positive meniscus lens of thefourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.6 mm.

Example 5

As shown in FIGS. 5A to 5C, the zoom optical system of Example 5comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the image side in the telephotoend than in the wide-angle end. The aperture stop S and the second lensunit G2 integrally and monotonously move toward the object side. Thethird lens unit G3 moves along a locus concave toward the object sidewhile increasing the space between the third lens unit and the secondlens unit G2, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The fourth lens unit G4 isfixed with respect to an image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, and a cemented lens of a biconvex positive lensand a biconcave negative lens. The third lens unit G3 constituted of onebiconvex positive lens, and the fourth lens unit G4 constituted of onepositive meniscus lens directing its concave surface on the object side.The aperture stop S is disposed between the biconvex positive lens andthe cemented lens of the biconvex positive lens and the biconcavenegative lens in the second lens unit G2.

Aspherical surfaces are used on five surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface of the biconvex positive single lens of the second lens unit G2;the image-side surface of the biconvex positive lens of the third lensunit G3; and the image-side surface of the positive meniscus lens of thefourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.6 mm.

Example 6

As shown in FIGS. 6A to 6C, the zoom optical system of Example 6comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to an image side in the telephotoend than in the wide-angle end. The aperture stop S and the second lensunit G2 integrally and monotonously move toward the object side. Thethird lens unit G3 slightly moves along a locus concave toward theobject side while increasing the space between the third lens unit andthe second lens unit G2, and is arranged slightly closer to the objectside in the telephoto end than in the wide-angle end. The fourth lensunit G4 is fixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, and a cemented lens of a biconvex positive lensand a biconcave negative lens. The third lens unit G3 constituted of onebiconvex positive lens, and the fourth lens unit G4 constituted of onepositive meniscus lens directing its concave surface on the object side.The aperture stop S is disposed between the biconvex positive lens andthe cemented lens of the biconvex positive lens and the biconcavenegative lens in the second lens unit G2.

Aspherical surfaces are used on seven surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; opposite surfaces ofthe biconvex positive single lens of the second lens unit G2; oppositesurfaces of the biconvex positive lens of the third lens unit G3; andthe image-side surface of the positive meniscus lens of the fourth lensunit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.6 mm.

Example 7

As shown in FIGS. 7A to 7C, the zoom optical system of Example 7comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to an image side in the telephotoend than in the wide-angle end. The aperture stop S and the second lensunit G2 integrally and monotonously move toward the object side. Thethird lens unit G3 moves along a locus concave toward the object sidewhile increasing the space between the third lens unit and the secondlens unit G2, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The fourth lens unit G4 isfixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, and a cemented lens of a biconvex positive lensand a biconcave negative lens. The third lens unit G3 constituted of onepositive meniscus lens directing its concave surface on the object side,and the fourth lens unit G4 constituted of one positive meniscus lensdirecting its concave surface on the object side. The aperture stop S isdisposed between the biconvex positive lens and the cemented lens of thebiconvex positive lens and the biconcave negative lens in the secondlens unit G2.

Aspherical surfaces are used on five surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface of the positive single lens of the second lens unit G2; theimage-side surface of the positive meniscus lens of the third lens unitG3; and the object-side surface of the positive meniscus lens of thefourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.6 mm.

Example 8

As shown in FIGS. 8A to 8C, the zoom optical system of Example 8comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to an image side in the telephotoend than in the wide-angle end. The aperture stop S and the second lensunit G2 integrally and monotonously move toward the object side. Thethird lens unit G3 moves along a locus concave toward the object sidewhile increasing the space between the third lens unit and the secondlens unit G2, and is arranged slightly closer to the image side in thetelephoto end than in the wide-angle end. The fourth lens unit G4 isfixed with respect to an image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, and a cemented lens of a biconvex positive lensand a biconcave negative lens. The third lens unit G3 constituted of onepositive meniscus lens directing its concave surface on the object side,and the fourth lens unit G4 constituted of one positive meniscus lensdirecting its concave surface on the object side. The aperture stop S isdisposed between the biconvex positive lens and the cemented lens of thebiconvex positive lens and the biconcave negative lens in the secondlens unit G2.

Aspherical surfaces are used on six surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; opposite surfaces ofthe positive single lens of the second lens unit G2; theimage-surface-side surface of the positive meniscus lens of the thirdlens unit G3; and the object-side surface of the positive meniscus lensof the fourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 9

As shown in FIGS. 9A to 9C, the zoom optical system of Example 9comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the image side in the telephotoend than in the wide-angle end. The aperture stop S and the second lensunit G2 integrally and monotonously move toward the object side. Thethird lens unit G3 moves along a locus concave toward the object sidewhile increasing the space between the third lens unit and the secondlens unit G2, and is arranged slightly closer to the image side in thetelephoto end than in the wide-angle end. The fourth lens unit G4 isfixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, and a cemented lens of a biconvex positive lensand a biconcave negative lens. The third lens unit G3 constituted of onepositive meniscus lens directing its concave surface on the object side,and the fourth lens unit G4 constituted of one positive meniscus lensdirecting its concave surface on the object side. The aperture stop S isdisposed on the object side of the second lens unit G2.

Aspherical surfaces are used on six surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; opposite surfaces ofthe positive single lens of the second lens unit G2; the image-sidesurface of the positive meniscus lens of the third lens unit G3; and theobject-side surface of the positive meniscus lens of the fourth lensunit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 10

As shown in FIGS. 10A to 10C, the zoom optical system of Example 10comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The aperture stop S and thesecond lens unit G2 integrally and monotonously move toward the objectside. The third lens unit G3 moves along a locus concave toward theobject side while increasing the space between the third lens unit andthe second lens unit G2, and is arranged slightly closer to the imageside in the telephoto end than in the wide-angle end. The fourth lensunit G4 is fixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, and a cemented lens of a biconvex positive lensand a biconcave negative lens. The third lens unit G3 constituted of onepositive meniscus lens directing its concave surface on the object side,and the fourth lens unit G4 constituted of one positive meniscus lensdirecting its concave surface on the object side. The aperture stop S isdisposed on the image side of the second lens unit G2.

Aspherical surfaces are used on six surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; opposite surfaces ofthe positive single lens of the second lens unit G2; the image-sidesurface of the positive meniscus lens of the third lens unit G3; and theobject-side surface of the positive meniscus lens of the fourth lensunit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 11

As shown in FIGS. 11A to 11C, the zoom optical system of Example 11comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The aperture stop S and thesecond lens unit G2 integrally and monotonously move toward the objectside. The third lens unit G3 monotonously moves toward the image sidewhile increasing the space between the third lens unit and the secondlens unit G2, and the fourth lens unit G4 is fixed with respect to theimage surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lens, a positive meniscus lens directing its convexsurface on the object side and a cemented lens of a positive meniscuslens directing its convex surface on the object side and a negativemeniscus lens directing its convex surface on the object side. The thirdlens unit G3 constituted of one biconvex positive lens, and the fourthlens unit G4 constituted of one biconvex positive lens. The aperturestop S is disposed between the positive meniscus lens directing itsconvex surface on the object side and the cemented lens in the secondlens unit G2.

Aspherical surfaces are used on six surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; opposite surfaces ofthe biconvex positive lens of the second lens unit G2; the image-sidesurface of the biconvex positive lens of the third lens unit G3; and anobject-side surface of the biconvex positive lens of the fourth lensunit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 12

As shown in FIGS. 12A to 12C, the zoom optical system of Example 12comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a negative refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The aperture stop S and thesecond lens unit G2 integrally and monotonously move toward the objectside. The third lens unit G3 monotonously moves toward the image sidewhile increasing the space between the third lens unit and the secondlens unit G2, and the fourth lens unit G4 is fixed with respect to theimage surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side,two biconvex positive lenses, and a negative meniscus lens directing itsconvex surface on the object side. The third lens unit G3 constituted ofone positive meniscus lens directing its convex surface on the imageside, and the fourth lens unit G4 constituted of one negative meniscuslens directing its convex surface on the image side. The aperture stop Sis disposed between the biconvex positive lens on the image side and thenegative lens in the second lens unit G2.

Aspherical surfaces are used on seven surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; opposite surfaces ofthe biconvex positive lens on the object side in the second lens unitG2; the image-side surface of the positive meniscus lens of the thirdlens unit G3; and opposite surfaces of the negative meniscus lens of thefourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 13

As shown in FIGS. 13A to 13C, the zoom optical system of Example 13comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a negative refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The aperture stop S and thesecond lens unit G2 integrally and monotonously move toward the objectside. The third lens unit G3 moves along a locus concave toward theobject side while increasing the space between the third lens unit andthe second lens unit G2. The third lens unit is arranged slightly closerto the image side in the telephoto end than in the wide-angle end. Thefourth lens unit G4 is fixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, abiconvex positive lenses, a positive meniscus lens directing its convexsurface on the object side and a negative meniscus lens directing itsconvex surface on the object side. The third lens unit G3 constituted ofone positive meniscus lens directing its convex surface on the imageside, and the fourth lens unit G4 constituted of one negative meniscuslens directing its convex surface on the image side. The aperture stop Sis disposed between the positive meniscus lens directing its convexsurface on the object side and the negative lens in the second lens unitG2.

Aspherical surfaces are used on six surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; opposite surfaces ofthe biconvex positive lens of the second lens unit G2; the image-sidesurface of the biconvex positive lens of the third lens unit G3; and theobject-side surface of the negative meniscus lens of the fourth lensunit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 14

As shown in FIGS. 14A to 14C, the zoom optical system of Example 14comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The aperture stop S and thesecond lens unit G2 integrally and monotonously move toward the objectside. The third lens unit G3 monotonously moves toward the image sidewhile increasing the space between the third lens unit and the secondlens unit G2, and the fourth lens unit G4 is fixed with respect to theimage surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, acemented lens of a positive meniscus lens directing its convex surfaceon the object side and a biconvex positive lens, and a cemented lens ofa positive meniscus lens directing its convex surface on the object sideand a negative meniscus lens directing its convex surface on the objectside. The third lens unit G3 constituted of one positive meniscus lensdirecting its convex surface on the image side, and the fourth lens unitG4 constituted of one positive meniscus lens directing its convexsurface on the image side. The aperture stop S is disposed between twocemented lenses of the second lens unit G2.

Aspherical surfaces are used on six surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface and the image-side surface of the cemented lens on the objectside in the second lens unit G2; the image-side surface of the positivemeniscus lens of the third lens unit G3; and the object-side surface ofthe positive meniscus lens of the fourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 15

As shown in FIGS. 15A to 15C, the zoom optical system of Example 15comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit C2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a positive refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the image side in the telephotoend than in the wide-angle end. The aperture stop S and the second lensunit G2 integrally and monotonously move toward the object side. Thethird lens unit G3 moves along a locus concave toward the object sidewhile increasing the space between the third lens unit and the secondlens unit G2, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end, and the fourth lens unit G4 isfixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, acemented lens of a biconvex positive lens and a negative meniscus lensdirecting its convex surface on the image side, and a cemented lens of abiconvex positive lens and a biconcave negative lens. The third lensunit G3 constituted of one biconvex positive lens, and the fourth lensunit G4 constituted of one positive meniscus lens directing its convexsurface on the image side. The aperture stop S is disposed between twocemented lenses of the second lens unit G2.

Aspherical surfaces are used on five surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface of the cemented lens on the object side in the second lens unitG2; the image-side surface of the biconvex positive lens of the thirdlens unit G3; and the object-side surface of the positive meniscus lensof the fourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 16

As shown in FIGS. 16A to 16C, the zoom optical system of Example 16comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a negative refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the image side in the telephotoend than in the wide-angle end. The aperture stop S and the second lensunit G2 integrally and monotonously move toward the object side. Thethird lens unit G3 moves along a locus concave toward the object sidewhile increasing the space between the third lens unit and the secondlens unit G2, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The fourth lens unit G4 isfixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, acemented lens of a biconvex positive lens and a negative meniscus lensdirecting its convex surface on the image side, and a negative meniscuslens directing its convex surface on the object side. The third lensunit G3 constituted of one positive meniscus lens directing its convexsurface on the image side, and the fourth lens unit G4 constituted ofone biconcave negative lens. The aperture stop S is disposed between thecemented lens and the negative meniscus lens directing its convexsurface on the object side in the second lens unit G2.

Aspherical surfaces are used on five surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface of the biconvex positive lens of the second lens unit G2; theimage-side surface of the positive meniscus lens of the third lens unitG3; and the object-side surface of the biconcave negative lens of thefourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 17

As shown in FIGS. 17A to 17C, the zoom optical system of Example 17comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a negative refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The aperture stop S and thesecond lens unit G2 integrally and monotonously move toward the objectside. The third lens unit G3 moves along a locus concave toward theobject side while increasing the space between the third lens unit andthe second lens unit G2, and is arranged slightly closer to the imageside in the telephoto end than in the wide-angle end. The fourth lensunit G4 is fixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, acemented lens of a biconvex positive lens and a negative meniscus lensdirecting its convex surface on the image side and a negative meniscuslens directing its convex surface on the object side. The third lensunit G3 constituted of one positive meniscus lens directing its convexsurface on the image side, and the fourth lens unit G4 constituted of abiconcave negative lens. The aperture stop S is disposed between thecemented lens and the negative meniscus lens directing its convexsurface on the object side in the second lens unit G2.

Aspherical surfaces are used on five surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface of the biconvex positive lens of the second lens unit G2; theimage-side surface of the positive meniscus lens of the third lens unitG3; and the object-side surface of the biconcave negative lens of thefourth lens unit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

Example 18

As shown in FIGS. 18A to 18C, the zoom optical system of Example 18comprises, in order from the object side: a first lens unit G1 having anegative refractive power; a second lens unit G2 having a positiverefractive power; a third lens unit G3 having a positive refractivepower; and a fourth lens unit G4 having a negative refractive power.When zooming is performed from the wide-angle end to the telephoto end,the first lens unit G1 moves along a locus concave toward the objectside, and is arranged slightly closer to the object side in thetelephoto end than in the wide-angle end. The aperture stop S and thesecond lens unit C2 integrally and monotonously move toward the objectside. The third lens unit G3 moves along a locus concave toward theobject side while increasing the space between the third lens unit andthe second lens unit G2, and is arranged slightly closer to the imageside in the telephoto end than in the wide-angle end. The fourth lensunit G4 is fixed with respect to the image surface I.

The first lens unit G1 constituted of one biconcave negative lens, andthe second lens unit G2 constituted of, in order from the object side, acemented lens of a biconvex positive lens and a negative meniscus lensdirecting its concave surface on the object side, and a negativemeniscus lens directing its convex surface on the object side. The thirdlens unit G3 constituted of one positive meniscus lens directing itsconcave surface on the object side, and the fourth lens unit G4constituted of one negative meniscus lens directing its concave surfaceon the object side. The aperture stop S is disposed between the cementedlens and the negative meniscus lens directing its convex surface on theobject side in the second lens unit G2.

Aspherical surfaces are used on five surfaces: opposite surfaces of thebiconcave negative lens of the first lens unit G1; the object-sidesurface of the biconvex lens of the second lens unit G2; the image-sidesurface of the positive meniscus lens of the third lens unit G3; and theobject-side surface of the negative meniscus lens of the fourth lensunit G4.

It is to be noted that the diagonal length of the effective image takingregion of the image sensor disposed on the image surface I is 7.2 mm.

As described above in Examples 1 to 18, the aperture stop S may bedisposed between the lenses of the second lens unit G2, and the aperturestop S may be a variable aperture stop. Alternatively, the apertureshape of this aperture stop S is fixed, and an aperture stop which has avariable aperture and moves integrally with the second lens unit G2along the optical axis may be disposed immediately before the secondlens unit G2. In such constitution, the aperture stop is disposed in anintermediate position of the optical system in a bright state with areduced F number. Therefore, even in a state in which a space betweenthe lenses of the second lens unit G2 is reduced, an effective diameteris easily balanced, a quantity of light can be adjusted by the aperturestop immediately before the second lens unit G2, and the constitution isadvantageous in the miniaturization and the improvement of performance.

There will be described hereinafter numeric value data of the aboveexamples. In addition to the above-described symbols, f denotes a focallength of the zoom optical system, FNO denotes the F number, ω is a halfangle of field, WE denotes the wide-angle end, ST denotes theintermediate state, TE denotes the telephoto end, R denotes a radius ofcurvature of each lens surface, D denotes a space between the lenssurfaces, Nd denotes a refractive index of each lens for the wavelengthof the d-line, and Vd denotes the Abbe number of each lens. It is to benoted that an aspherical shape is represented by the following equationin a coordinate system in which x axis coincide with the optical axishaving the positive direction toward the light traveling direction, andy axis is set to be perpendicular to the optical axis and to intersectwith the optical axis at the vertex of the aspherical surface.x=(y ² /r)/[1+{1−(k+1)(y/r)²}^(1/2) ]+A4·y ⁴ +A6·y ⁶ +A8·y ⁸ +A10·y ¹⁰,wherein r denotes a paraxial radius of curvature, k denotes a coniccoefficient, and A4, A6, A8 and A10 denote fourth-order, sixth-order,eighth-order and tenth-order aspherical coefficients, respectively.

It is to be noted that in data tables, e means a power of 10. Therefore,in Example 1, the value 2.5934e−4 of the aspherical coefficient A4 ofthe first surface may also be written as 2.5934×10⁻⁴.

Example 1

TABLE 1 Surface R D Nd Vd 1 −11.92 (ASP) 0.90 1.49585 81.29 2  27.33(ASP) D2 3  4.68 (ASP) 1.53 1.80610 40.73 4 −18.01 (ASP) 0.10 5 ∞ (STOP)0.20 6 18.23 1.13 1.78800 47.37 7 −18.23 0.50 1.80518 25.42 8 3.25 D8 9−100.00 2.39 1.52542 55.78 10  −6.38 (ASP) D10 11 −11.61 (ASP) 1.0 1.52542 55.78 12 −10.00 0.13 13 ∞ 0.40 1.54771 62.84 14 ∞ 0.20 15 ∞ 0.501.51633 64.14 16 ∞ 0.4  17 ∞ (IS) (ASP): Aspherical surface (IS): Imagesurface

TABLE 2 Aspherical Coefficient Sur- face k A4 A6 A8 A10 1 −8.75492.5934e−4 −1.0324e−5 1.9658e−7 −1.1823e−9 2 −5.5621 6.5808e−4 −1.0089e−5−1.4087e−7 8.9371e−9 3 −0.9814 5.0935e−4 −2.0108e−5 0 0 4 26.80181.7431e−3 −3.1339e−5 0 0 10 −2.0433 −3.7794e−4 −2.5613e−7 2.3576e−7−2.2294e−9 11 −0.9892 −2.1476e−3 6.9184e−5 −1.2423e−7 0

TABLE 3 Zoom Data (∞) WE ST TE f 6.5 10.8 18.7 FNO 3.2 4.2 6.0 2ω 60.2435.61 21.08 D2 13.03 6.81 2.33 D8 2.78 6.92 13.33 D10 2.58 2.28 2.55

Example 2

TABLE 4 Surface R D Nd Vd 1 −10.52 (ASP)  0.90 1.49700 81.54 2 65.93(ASP) D2 3  5.67 (ASP) 1.24 1.80610 40.92 4 −64.38 0.10 5 ∞ (STOP) 0.166 7.27 1.60 1.80610 40.92 7 −11.61 0.01 1.56384 60.67 8 −11.61 0.601.80518 25.42 9 3.13 D9 10 −26.48 1.96 1.52542 55.78 11 −7.95 (ASP) D1112 12.66 (ASP) 0.80 1.52542 55.78 13 87.29 0.50 14 ∞ 0.40 1.54771 62.8415 ∞ 0.50 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.49 18 ∞ (IS) (ASP): Asphericalsurface (IS): Image surface

TABLE 5 Aspherical Coefficient Sur- face k A4 A6 A8 A10 1 −2.04116.7069e−4 −7.8503e−6 −1.8300e−7 3.4301e−9 2 −3.2798 5.0207e−4 1.5198e−5−1.1126e−6 1.4226e−8 3 −1.8486 4.0743e−4 6.9464e−5 −1.3137e−5 0.0000 11−1.1386 −3.2091e−4 −1.9734e−5 5.8425e−7 0.0000 12 −52.2476 1.1369e−3−1.1048e−4 2.6042e−6 0.0000

TABLE 6 Zoom Data (∞) WE ST TE f 6.5 10.8 18.7 FNO 3.3 4.3 6.0 2ω 63.6237.50 22.25 D2 13.21 6.20 1.21 D9 2.35 6.06 11.49 D11 2.29 1.79 2.14

Example 3

TABLE 7 Surface R D Nd Vd 1 −10.44 (ASP)  0.92 1.49700 81.54 2 65.67(ASP) D2 3  5.64 (ASP) 1.24 1.80610 40.92 4 −63.90 0.10 5 ∞ (STOP) 0.166 7.22 1.59 1.80440 39.59 7 −11.06 0.01 1.56384 60.67 8 −11.06 0.601.80518 25.42 9 3.13 D9 10 −21.26 1.95 1.52542 55.78 11 −7.04 (ASP) D1112 18.90 (ASP) 0.81 1.52542 55.78 13 71.91 (ASP) 0.51 14 ∞ 0.40 1.5477162.84 15 ∞ 0.50 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.54 18 ∞ (IS) (ASP):Aspherical surface (IS): Image surface

TABLE 8 Aspherical Coefficient Sur- face k A4 A6 A8 A10 1 −2.60127.8726e−4 −5.6369e−6 −2.4476e−7 3.2708e−9 2 −2.4886 6.9673e−4 2.0024e−5−1.0587e−6 7.8232e−9 3 −1.7671 3.6415e−4 4.0846e−5 −3.9529e−6 0.0000 11−3.9944 −2.6447e−4 −6.5077e−5 1.3413e−6 0.0000 12 −275.4350 1.3787e−3−1.1378e−4 2.8956e−7 0.0000 13 0.0000 −8.3229e−4 −1.4075e−8 0.00000.0000

TABLE 9 Zoom Data (∞) WE ST TE f 6.5 10.9 18.6 FNO 3.3 4.3 6.0 2ω 63.3337.33 22.40 D2 13.49 6.24 1.50 D9 2.42 6.03 11.55 D11 2.10 1.62 1.31

Example 4

TABLE 10 Surface R D Nd Vd 1 −10.49 (ASP)  0.90 1.49700 81.54 2 65.24(ASP) D2 3  5.67 (ASP) 1.23 1.80610 40.92 4 −64.32 0.10 5 ∞ (STOP) 0.156 7.25 1.65 1.80440 39.59 7 −10.47 0.01 1.56384 60.67 8 −10.47 0.601.80518 25.42 9 3.13 D9 10 −19.58 1.94 1.52542 55.78 11 −5.63 (ASP) D1112 50.00 (ASP) 0.90 1.52542 55.78 13 100.00 (ASP)  0.25 14 ∞ 0.401.54771 62.84 15 ∞ 0.23 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.15 18 ∞ (IS)(ASP): Aspherical surface (IS): Image surface

TABLE 11 Aspherical Coefficient Sur- face k A4 A6 A8 A10 1 −3.31928.7761e−4 −9.8061e−6 −2.3171e−7 3.7785e−9 2 −3.6455 8.0979e−4 1.8372e−5−1.2379e−6 1.0317e−8 3 −1.8265 4.0328e−4 6.7966e−5 −1.2220e−5 0.0000 11−3.7461 −3.6121e−4 −5.5086e−5 1.1366e−6 1.1521e−8 12 −17.8241 3.0854e−3−2.0462e−4 5.6111e−7 0.0000 13 0 1.3146e−8 1.0851e−7 0.0000 0.0000

TABLE 12 Zoom Data (∞) WE ST TE f 6.3 10.7 18.6 FNO 3.3 4.4 6.0 2ω 63.5536.96 21.85 D2 13.36 6.08 1.18 D9 2.17 5.98 11.46 D11 2.85 2.30 2.76

Example 5

TABLE 13 Surface R D Nd Vd 1 −16.49 (ASP) 0.90 1.49700 81.54 2  17.47(ASP) D2 3  5.89 (ASP) 1.31 1.80610 40.92 4 −48.57 0.10 5 ∞ (STOP) 0.386 7.66 1.47 1.80610 40.92 7 −12.35 0.01 1.56384 60.67 8 −12.35 0.601.80518 25.42 9 3.30 D9 10 40.76 2.22 1.52542 55.78 11 −10.80 (ASP)  D1112 −34.89 0.90 1.52542 55.78 13 −11.57 (ASP) 0.25 14 ∞ 0.40 1.5477162.84 15 ∞ 0.23 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.36 18 ∞ (IS) (ASP):Aspherical surface (IS): Image surface

TABLE 14 Aspherical Coefficient Surface k A4 A6 A8 A10 1 6.27134.6281e−4 7.9660e−6 −5.0117e−7 1.1488e−8 2 −14.3023 4.3131e−4 2.0709e−5−1.5374e−6 2.6027e−8 3 −2.2930 8.4979e−4 −6.2420e−5 6.2228e−6 0.0000 11−13.6395 −7.9925e−4 −2.1441e−5 1.4054e−6 −2.0937e−8 13 2.6268 1.1029e−38.6287e−5 −2.4783e−6 0.0000

TABLE 15 Zoom Data (∞) WE ST TE f 6.6 10.9 18.6 FNO 3.3 4.3 6.0 2ω 63.1137.08 22.36 D2 13.06 6.49 2.09 D9 2.77 6.60 12.69 D11 2.49 2.36 2.67

Example 6

TABLE 16 Surface R D Nd Vd 1 −10.66 (ASP) 0.90 1.49700 81.54 2  38.12(ASP) D2 3  5.12 (ASP) 1.38 1.80610 40.92 4 −30.30 (ASP) 0.10 5 ∞ (STOP)0.31 6 9.69 1.31 1.80610 40.92 7 −11.15 0.01 1.56384 60.67 8 −11.15 0.601.80518 25.42 9 3.09 D9 10 220.69 (ASP) 2.26 1.52542 55.78 11  −8.44(ASP)  D11 12 −264.24 0.90 1.52542 55.78 13 −20.73 (ASP) 0.13 14 ∞ 0.401.54771 62.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.36 18 ∞ (IS)(ASP): Aspherical surface (IS): Image surface

TABLE 17 Aspherical Coefficient Surface k A4 A6 A8 A10 1 2.09549.9284e−4 1.4292e−5 −9.7552e−7 2.0293e−8 2 −100.2558 6.8011e−4 2.7395e−5−1.7990e−6 2.1020e−8 3 −3.8250 2.8008e−3 −1.3642e−4 1.8252e−6 0.0000 4−324.9321 −1.1098e−3 2.5674e−4 −3.4578e−5 0.0000 10 178.1632 5.1733e−40.0000 0.0000 0.0000 11 −4.8466 1.1801e−4 −3.9709e−5 1.7420e−6−2.2736e−8 13 −14.3108 −6.3158e−4 1.5915e−4 −3.9176e−6 0.0000

TABLE 18 Zoom Data (∞) WE ST TE f 6.5 10.7 18.6 FNO 3.3 4.3 6.0 2ω 63.3938.14 22.65 D2 13.07 6.93 1.90 D9 2.82 6.77 12.24 D11 2.41 1.93 2.95

Example 7

TABLE 19 Surface R D Nd Vd 1 −14.12 (ASP) 0.90 1.49700 81.54 2  21.36(ASP) D2 3  5.06 (ASP) 1.34 1.80610 40.92 4 −28.73 0.10 5 ∞ (STOP) 0.216 9.71 1.33 1.80440 39.59 7 −9.90 0.01 1.56384 60.67 8 −9.90 0.601.80518 25.42 9 3.06 D9 10 −61.52 2.35 1.52542 55.78 11  −6.61 (ASP) D11 12 −11.51 (ASP) 1.00 1.52542 55.78 13 −8.59 0.13 14 ∞ 0.40 1.5477162.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.42 18 ∞ (IS) (ASP):Aspherical surface (IS): Image surface

TABLE 20 Aspherical Coefficient Surface k A4 A6 A8 A10 1 0.75161.2358e−5 1.6437e−5 −2.3080e−7 −6.5270e−10 2 4.2647 −2.3091e−4 9.5848e−67.5350e−7 −2.5412e−8 3 −1.8544 7.5794e−4 −3.3738e−5 0.0000 0.0000 11−0.9391 −8.6045e−5 1.9294e−6 −1.2024e−6 4.1048e−8 12 0 −1.9309e−33.2847e−5 0.0000 0.0000

TABLE 21 Zoom Data (∞) WE ST TE f 6.5 10.7 18.6 FNO 3.3 4.3 6.0 2ω 64.0738.20 22.64 D2 13.21 7.02 1.98 D9 2.66 6.58 12.06 D11 2.38 1.85 2.44

Example 8

TABLE 22 Surface R D Nd Vd 1 −12.342 (ASP) 0.90 1.49585 81.29 2  24.778(ASP) D2 3  4.605 (ASP) 1.53 1.80610 40.92 4 −19.256 (ASP) 0.10 5 ∞(STOP) 0.20 6 18.633 1.08 1.78800 47.37 7 −18.633 0.01 1.56384 60.67 8−18.633 0.50 1.80518 25.42 9 3.297 D9 10 −70.515 2.34 1.52542 55.78 11 −6.314 (ASP)  D11 12 −11.608 (ASP) 1.00 1.52542 55.78 13 −10.178 0.1314 ∞ 0.40 1.54771 62.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.37 18 ∞(IS) (ASP): Aspherical surface (IS): Image surface

TABLE 23 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −14.452−7.36680e−05 −5.39210e−06 2.67986e−07 −3.93094e−09 2 1.669 6.12523e−04−3.17858e−05 1.00832e−06 −1.31321e−08 3 0.050 −7.13822e−04 1.59206e−050.0000 0.0000 4 39.707 1.97205e−03 8.50652e−05 0.0000 0.0000 11 −2.436−4.92654e−04 −1.21534e−06 5.08409e−07 −9.44459e−09 12 −2.062−2.07213e−03 6.44774e−05 1.64310e−07 0.0000

TABLE 24 Zoom Data WE ST TE f 6.51 10.85 18.59 FNO 3.18 4.26 6.00 2ω60.57 35.62 21.18 D2 12.97 6.84 2.43 D9 2.79 7.00 13.35 D11 2.66 2.322.55

Example 9

TABLE 25 Surface R D Nd Vd 1 −12.342 (ASP) 0.90 1.49585 81.29 2  24.778(ASP) D2 3 ∞ (STOP) 0.00 4  4.605 (ASP) 1.53 1.80610 40.92 5 −19.256(ASP) 0.30 6 18.633 1.08 1.78800 47.37 7 −18.633 0.01 1.56384 60.67 8−18.633 0.50 1.80518 25.42 9 3.297 D9 10 −70.515 2.34 1.52542 55.78 11 −6.314 (ASP)  D11 12 −11.608 (ASP) 1.00 1.52542 55.78 13 −10.178 0.1314 ∞ 0.40 1.54771 62.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.37 18 ∞(IS) (ASP): Aspherical surface (IS): Image surface

TABLE 26 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −14.452−7.36680e−05 −5.39210e−06 2.67986e−07 −3.93094e−09 2 1.669 6.12523e−04−3.17858e−05 1.00832e−06 −1.31321e−08 4 0.050 −7.13822e−04 1.59206e−050.0000 0.0000 5 39.707 1.97205e−03 8.50652e−05 0.0000 0.0000 11 −2.436−4.92654e−04 −1.21534e−06 5.08409e−07 −9.44459e−09 12 −2.062−2.07213e−03 6.44774e−05 1.64310e−07 0.0000

TABLE 27 Zoom Data WE ST TE f 6.51 10.85 18.59 FNO 3.25 4.30 6.00 2ω60.57 35.62 21.18 D2 12.97 6.84 2.43 D9 2.80 7.00 13.35 D11 2.66 2.322.55

Example 10

TABLE 28 Surface R D Nd Vd 1 −12.342 (ASP) 0.90 1.49585 81.29 2  24.778(ASP) D2 3  4.605 (ASP) 1.53 1.80610 40.92 4 −19.256 (ASP) 0.30 5 18.6331.08 1.78800 47.37 6 −18.633 0.01 1.56384 60.67 7 −18.633 0.50 1.8051825.42 8 3.297 0.50 9 ∞ (STOP) D9 10 −70.515 2.34 1.52542 55.78 11 −6.314 (ASP)  D11 12 −11.608 (ASP) 1.00 1.52542 55.78 13 −10.178 0.1314 ∞ 0.40 1.54771 62.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.37 18 ∞(IS) (ASP): Aspherical surface (IS): Image surface

TABLE 29 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −14.452−7.36680e−05 −5.39210e−06 2.67986e−07 −3.93094e−09 2 1.669 6.12523e−04−3.17858e−05 1.00832e−06 −1.31321e−08 3 0.050 −7.13822e−04 1.59206e−050.0000 0.0000 4 39.707 1.97205e−03 8.50652e−05 0.0000 0.0000 11 −2.436−4.92654e−04 −1.21534e−06 5.08409e−07 −9.44459e−09 12 −2.062−2.07213e−03 6.44774e−05 1.64310e−07 0.0000

TABLE 30 Zoom Data WE ST TE f 6.51 10.85 18.59 FNO 3.03 4.15 6.00 2ω60.50 35.59 21.17 D2 12.97 6.84 2.43 D9 2.30 6.50 12.85 D11 2.66 2.322.55

Example 11

TABLE 31 Surface R D Nd Vd 1 −12.632 (ASP) 0.90 1.49585 81.29 2  48.824(ASP) D2  3  5.846 (ASP) 1.46 1.80610 40.92 4 −47.738 (ASP) 0.05 5 6.3901.03 1.51633 64.14 6 105.180 0.05 7 ∞ (STOP) 0.10 8 89.402 0.81 1.7880047.37 9 266.679 0.01 1.56384 60.67 10 266.679 0.50 1.80518 25.42 113.211 D11 12 431.826 2.82 1.52542 55.78 13  −6.529 (ASP) D13 14  29.544(ASP) 1.00 1.52542 55.78 15 −2115.094 0.18 16 ∞ 0.40 1.54771 62.84 17 ∞0.20 18 ∞ 0.50 1.51633 64.14 19 ∞ 0.37 20 ∞ (IS) (ASP): Asphericalsurface (IS): Image surface

TABLE 32 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −4.6011.44022e−04 −1.15649e−05 2.38162e−07 −1.48559e−09 2 64.783 1.37819e−04−1.45767e−05 2.73389e−07 −2.67809e−09 3 −0.814 −1.62814e−05 −2.80654e−050.0000 0.0000 4 27.287 1.43091e−04 −3.59649e−05 0.0000 0.0000 13 −3.476−7.88267e−04 2.36626e−05 −5.40533e−07 9.37644e−09 14 −708.771−1.09477e−05 −4.94946e−05 2.45570e−06 0.0000

TABLE 33 Zoom Data WE ST TE f 6.50 12.85 24.92 FNO 2.88 4.36 6.90 2ω60.73 29.88 16.09 D2 15.16 6.28 1.11 D11 2.26 8.50 17.96 D13 2.41 1.711.36

Example 12

TABLE 34 Surface R D Nd Vd 1 −9.944 (ASP) 0.90 1.49700 81.54 2 7401.919(ASP) D2 3 6.282 (ASP) 1.22 1.80610 40.92 4 −857.948 (ASP) 0.10 5 6.2061.15 1.51633 64.14 6 −5697.765 0.10 7 ∞ (STOP) 0.10 8 31.899 1.061.80518 25.42 9 3.499 D9 10 −438.020 2.74 1.52542 55.78 11 −5.870 (ASP)D11 12 −12.016 (ASP) 1.00 1.52542 55.78 13 −76.944 (ASP) 0.10 14 ∞ 0.401.54771 62.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.37 18 ∞ (IS)(ASP): Aspherical surface (IS): Image surface

TABLE 35 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −5.3612.91000e−04 −3.55384e−06 −1.46834e−08 4.48856e−10 2 −54123780.0085.95382e−04 −5.04980e−06 −3.48145e−08 7.20173e−10 3 −0.538 5.56671e−05−9.97132e−06 9.92000e−07 0.0000 4 −1793111.847 2.95826e−04 1.93546e−06−7.03818e−08 0.0000 11 −3.691 −8.73664e−04 1.38603e−05 −2.07023e−072.82176e−09 12 3.531 −3.47723e−03 1.13536e−04 1.61584e−06 −2.03470e−0813 193.221 −3.84220e−03 3.42955e−05 6.55069e−06 −7.12518e−08

TABLE 36 Zoom Data WE ST TE f 6.56 12.67 25.86 FNO 2.86 4.33 6.90 2ω60.02 30.45 15.26 D2 16.51 7.34 1.23 D9 2.49 8.69 18.98 D11 2.86 2.191.90

Example 13

TABLE 37 Surface R D Nd Vd 1 −9.550 ASP 0.90 1.49700 81.54 2 7436.537(ASP) D2 3 6.077 (ASP) 1.52 1.80610 40.92 4 −150.366 (ASP) 0.10 5 6.5261.36 1.48749 70.23 6 37.335 0.10 7 ∞ (STOP) 0.10 8 24.486 1.12 1.8466623.78 9 3.563 D9 10 −23.541 2.36 1.52542 55.78 11 −5.492 (ASP) D11 12−7.930 (ASP) 1.00 1.52542 55.78 13 −12.641 (ASP) 0.13 14 ∞ 0.40 1.5477162.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.37 18 ∞ (IS) (ASP):Aspherical surface (IS): Image surface

TABLE 38 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −4.2524.46874e−04 −3.21208e−06 −1.25897e−08 1.39474e−10 2 −473170157.3337.68713e−04 −4.88083e−06 1.15119e−07 −2.11027e−09 3 −0.321 1.92387e−04−1.64944e−05 8.18573e−06 0.0000 4 −17580.141 2.40113e−04 5.33829e−055.75258e−06 0.0000 11 −3.213 −8.34348e−04 1.29221e−05 −5.00650e−078.93581e−09 12 −22.737 −2.69634e−03 9.89730e−05 8.97548e−07 −3.19078e−0713 −160.409 −1.91887e−03 6.30689e−05 3.18460e−06 −3.24049e−07

TABLE 39 Zoom Data WE ST TE f 6.58 13.77 31.16 FNO 2.92 4.60 8.00 2ω59.56 28.28 12.73 D2 18.81 7.94 1.22 D9 2.44 8.75 21.19 D11 2.88 2.132.33

Example 14

TABLE 40 Surface R D Nd Vd 1 −11.066 (ASP) 0.90 1.49585 81.29 2 47.944(ASP) D2 3 4.456 (ASP) 0.75 1.80610 40.92 4 4.735 0.01 1.56384 60.67 54.735 1.33 1.78800 47.37 6 −25.240 (ASP) 0.10 7 ∞ (STOP) 0.20 8 18.8920.93 1.78800 47.37 9 34.093 0.01 1.56384 60.67 10 34.093 0.50 1.8051825.42 11 3.340 D11 12 −32.885 2.45 1.52542 55.78 13 −6.702 (ASP) D13 14−61.572 (ASP) 1.00 1.52542 55.78 15 −11.075 0.13 16 ∞ 0.40 1.54771 62.8417 ∞ 0.20 18 ∞ 0.50 1.51633 64.14 19 ∞ 0.37 20 ∞ (IS) (ASP): Asphericalsurface (IS): Image surface

TABLE 41 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −7.418−2.17928e−05 −2.42677e−05 3.80713e−07 3.98078e−10 2 11.889 3.69338e−04−4.19483e−05 5.64048e−07 3.51294e−09 3 0.337 −9.33621e−04 3.63258e−050.0000 0.0000 6 6.161 2.00672e−03 1.31617e−04 0.0000 0.0000 13 −0.776−8.44178e−04 3.51523e−05 6.30475e−07 −2.93577e−08 14 195.474−6.69998e−03 3.95455e−04 −6.06401e−06 0.0000

TABLE 42 Zoom Data WE ST TE f 6.48 12.41 24.77 FNO 3.03 4.32 6.99 2ω62.53 31.16 16.58 D2 14.54 5.72 0.85 D11 2.65 7.54 17.12 D13 2.68 2.481.97

Example 15

TABLE 43 Surface R D Nd Vd 1 −11.535 (ASP) 0.92 1.52542 55.78 2 44.496(ASP) D2 3 5.974 (ASP) 1.43 1.80610 40.92 4 −9.711 0.01 1.56384 60.67 5−9.711 0.95 1.51633 64.14 6 −21.069 0.10 7 ∞ (STOP) 0.20 8 14.326 1.131.78800 47.37 9 −14.326 0.01 1.56384 60.67 10 −14.326 0.50 1.80518 25.4211 3.669 D11 12 61.202 2.31 1.52542 55.78 13 −8.645 (ASP) D13 14 −41.658(ASP) 1.00 1.52542 55.78 15 −14.560 0.13 16 ∞ 0.40 1.54771 62.84 17 ∞0.20 18 ∞ 0.50 1.51633 64.14 19 ∞ 0.37 20 ∞ (IS) (ASP): Asphericalsurface (IS): Image surface

TABLE 44 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −4.739−2.42892e−05 5.93100e−06 1.06044e−07 −7.34218e−09 2 −286.654 4.03482e−04−9.96697e−06 1.21655e−06 −3.75453e−08 3 −0.361 −7.83563e−04 −3.53928e−050.0000 0.0000 13 −5.933 −8.36717e−04 −3.42841e−05 2.37781e−06−4.11212e−08 14 −418.964 −2.41451e−03 −1.13925e−05 2.20868e−06 0.0000

TABLE 45 Zoom Data WE ST TE f 6.50 10.93 18.54 FNO 3.17 4.20 5.90 2ω60.65 35.19 21.24 D2 12.75 6.03 1.50 D11 2.40 6.36 12.39 D13 2.50 2.312.67

Example 16

TABLE 46 Surface R D Nd Vd 1 −16.722 (ASP) 0.92 1.52542 55.78 2 24.383(ASP) D2 3 5.978 (ASP) 1.78 1.80610 40.92 4 −7.110 0.01 1.56384 60.67 5−7.110 1.17 1.48749 70.23 6 −25.129 0.10 7 ∞ (STOP) 0.20 8 19.667 1.341.92286 18.90 9 3.966 D9 10 −72.976 2.46 1.52542 55.78 11 −5.477 (ASP)D11 12 −71.478 (ASP) 1.00 1.52542 55.78 13 58.292 0.23 14 ∞ 0.40 1.5477162.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.37 18 ∞ (IS) (ASP):Aspherical surface (IS): Image surface

TABLE 47 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −13.560−1.30819e−04 −4.39392e−06 3.95509e−07 −4.29437e−09 2 −4.801 8.85323e−05−9.61643e−06 4.34121e−07 3.74699e−09 3 −0.486 −8.31598e−04 −2.95169e−05−1.18596e−06 0.0000 11 −3.079 −7.41409e−04 −2.81216e−06 1.39026e−06−4.31410e−08 12 309.973 −4.76487e−04 2.74533e−05 8.84682e−07 0.0000

TABLE 48 Zoom Data WE ST TE f 6.53 11.18 19.53 FNO 3.08 4.22 6.00 2ω59.28 34.77 20.31 D2 14.14 7.02 1.64 D9 2.35 6.76 13.36 D11 2.27 1.882.35

Example 17

TABLE 49 Surface R D Nd Vd 1 −19.181 (ASP) 0.92 1.52542 55.78 2 21.906(ASP) D2 3 6.268 (ASP) 1.63 1.80610 40.92 4 −9.628 0.01 1.56384 60.67 5−9.628 1.28 1.48749 70.23 6 −36.586 0.10 7 ∞ (STOP) 0.20 8 15.142 1.591.92286 18.90 9 4.115 D9 10 −57.058 2.63 1.69350 53.21 11 −7.792 (ASP)D11 12 −133.522 (ASP) 1.00 1.52542 55.78 13 154.287 0.16 14 ∞ 0.401.54771 62.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.37 18 ∞ (IS)(ASP): Aspherical surface (IS): Image surface

TABLE 50 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −12.994−1.62330e−04 −5.98347e−06 3.89382e−07 −3.89826e−09 2 −1.612 −1.80218e−05−1.19773e−05 4.95776e−07 2.10340e−11 3 −0.289 −6.38433e−04 −2.17034e−054.50188e−07 0.0000 11 −4.538 −6.52811e−04 9.29476e−06 2.09845e−07−9.20293e−09 12 1032.803 −1.37679e−03 6.16885e−05 −4.02989e−07 0.0000

TABLE 51 Zoom Data WE ST TE f 6.52 12.55 25.07 FNO 3.04 4.50 7.09 2ω60.30 31.10 15.95 D2 16.37 7.85 1.56 D9 2.29 8.50 18.07 D11 2.80 1.762.11

Example 18

TABLE 52 Surface R D Nd Vd 1 −14.957 (ASP) 0.90 1.49700 81.54 2 27.924(ASP) D2 3 5.876 (ASP) 1.29 1.80610 40.92 4 −19.955 0.01 1.56384 60.67 5−19.955 0.64 1.48749 70.23 6 −34.624 0.10 7 ∞ (STOP) 0.20 8 12.534 2.141.92286 18.90 9 3.811 D9 10 −23.691 2.36 1.52542 55.78 11 −5.644 (ASP)D11 12 −18.529 (ASP) 1.00 1.52542 55.78 13 −29.667 0.29 14 ∞ 0.401.54771 62.84 15 ∞ 0.20 16 ∞ 0.50 1.51633 64.14 17 ∞ 0.37 18 ∞ (IS)(ASP): Aspherical surface (IS): Image surface

TABLE 53 Aspherical Coefficient Surface k A4 A6 A8 A10 1 −7.211−1.11916e−04 −2.65958e−06 3.43230e−07 −6.14939e−09 2 9.879 6.85835e−05−2.66199e−05 1.55893e−06 −2.75621e−08 3 −0.293 −5.00819e−04 −2.87026e−051.61429e−06 0.0000 11 −1.825 1.73237e−04 −2.95462e−05 1.14852e−06−1.86965e−08 12 10.769 −1.92977e−04 9.27715e−06 0.0000 0.0000

TABLE 54 Zoom Data WE ST TE f 6.59 14.07 31.61 FNO 2.94 4.69 8.00 2ω59.74 27.822 12.522 D2 18.44 8.35 1.17 D9 2.55 10.04 22.95 D11 2.96 1.512.30

FIGS. 19A to 36C show aberration diagrams of Examples 1 to 18 whenfocused on an infinite object. In these drawings, FIGS. 19A, 20A, 21A,22A, 23A, 24A, 25A, 26A, 27A, 28A, 29A, 30A, 31A, 32A, 33A, 34A, 35A and36A show a spherical aberration (SA), an astigmatism (AS), a chromaticaberration of magnification (CC) and a distortion (DT) in the wide-angleend. FIGS. 19B, 20B, 21B, 22B, 23B, 24B, 25B, 26B, 27B, 28B, 29B, 30B,31B, 32B, 33B, 34B, 35B and 36B show the above aberrations in theintermediate state. FIGS. 19C, 20C, 21C, 22C, 23C, 24C, 25C, 26C, 27C,28C, 29C, 30C, 31C, 32C, 33C, 34C, 35C and 36C show the aboveaberrations in the telephoto end. In the drawings, “FIY” (3.78 mm, 3.99mm) denotes a maximum image height. These aberration diagrams show anaberration situation to the maximum image height that is larger than theimage height Y′ which is a half of the diagonal length of the effectiveimage taking region.

The following tables 55-1 to 55-3 show values of the conditions (1) to(14) of Examples 1 to 18 described above.

TABLE 55-1 Example Condition 1 2 3 4 5 6 7 (1) −0.39 −0.72 −0.73 −0.72−0.03 −0.56 −0.20 (2) −0.02 −0.03 −0.04 −0.04 −0.01 −0.02 −0.01 (3)0.003 0.002 0.003 0.004 0.003 0.004 0.001 (4) −1.72 −1.92 −1.93 −1.94−1.76 −1.78 −1.81 (5) 2.87 2.87 2.86 2.95 2.83 2.86 2.86 (6) 1.48 1.451.44 1.48 1.46 1.44 1.44 (7) 4.69 5.61 5.57 6.16 4.72 4.64 4.97 (8) 1.141.86 1.99 1.81 0.58 0.93 1.24 (9) 1.19 1.13 1.13 1.19 1.20 1.19 1.21(10)  0.42 0.39 0.40 0.40 0.42 0.42 0.42 (11)  2.15 1.94 1.94 1.97 2.082.05 2.06 (12)  −1.65 −1.84 −1.84 −1.94 −1.67 −1.72 −1.73 (13)  −0.57−0.64 −0.65 −0.66 −0.59 −0.60 −0.60 (14)  −2.97 −3.16 −3.16 −3.21 −2.89−2.94 −2.96

TABLE 55-2 Con- di- Example tion 8 9 10 11 12 13 14 (1) −0.335 −0.335−0.335 −0.589 −0.997 −0.997 −0.625 (2) −0.012 −0.011 −0.019 −0.011−0.056 −0.086 −0.005 (3) 0.003 0.002 0.004 0.000 0.000 0.000 −0.001 (4)−1.711 −1.711 −1.711 −1.895 −1.795 −1.783 −1.831 (5) 2.856 2.856 2.8563.805 3.942 4.750 3.805 (6) 1.479 1.479 1.479 1.633 1.710 1.650 1.513(7) 4.649 4.649 4.649 6.649 6.908 8.250 5.211 (8) 1.197 1.197 1.1970.970 1.027 1.608 1.512 (9) 1.177 1.177 1.177 1.341 1.286 1.314 1.257(10)  0.412 0.412 0.412 0.352 0.326 0.277 0.330 (11)  2.128 2.128 2.1282.425 2.325 2.381 2.272 (12)  −1.619 −1.619 −1.619 −2.158 −2.347 −2.696−2.103 (13)  −0.567 −0.567 −0.567 −0.567 −0.595 −0.568 −0.553 (14) −2.928 −2.928 −2.928 −3.903 −4.244 −4.883 −3.803

TABLE 55-3 Example Condition 15 16 17 18 (1) −0.588 −0.186 −0.066 −0.302(2) −0.012 −0.007 −0.002 −0.009 (3) 0.001 0.001 −0.001 0.000 (4) −1.795−1.842 −1.799 −1.761 (5) 2.846 3.000 3.805 4.805 (6) 1.484 1.577 1.6501.695 (7) 5.204 6.546 7.243 7.847 (8) 0.753 1.162 1.316 1.625 (9) 1.3151.392 1.439 1.327 (10) 0.462 0.464 0.378 0.276 (11) 2.378 2.494 2.6032.403 (12) −1.728 −1.938 −2.275 −2.650 (13) −0.607 −0.646 −0.598 −0.552(14) −3.125 −3.472 −4.114 −4.800

In addition, the zoom optical system of the present invention can beused in an image taking apparatus which comprises an image formingoptical system and an electronic image sensor for receiving the image ofan object formed by the image taking optical system such as a CCD imagesensor to perform photographing, especially in a digital camera or avideo camera, or an information processing device such as a personalcomputer, a telephone, or especially a cellular phone. Embodiments ofthe image taking apparatus will be described hereinafter.

FIGS. 37 to 39 are conceptual diagrams of a digital camera in which thezoom optical system of the present invention is incorporated in a imageforming optical system. FIG. 37 is a front perspective view showing anappearance of a digital camera 40, FIG. 38 is a rear view of the digitalcamera, and FIG. 39 is a diagrammatically sectional plan view showingthe internal constitution of the digital camera 40. FIGS. 37 and 39 showthat the image forming optical system 41 is brought into a non-collapsedstate. In this example, the digital camera 40 includes: the imageforming optical system 41; a finder optical system 43 having a finderoptical path 44; a shutter release button 45; a flash lamp 46; a liquidcrystal display monitor 47; a focal length control button 61; a settingchange switch 62 and the like. When the image forming optical system 41is collapsed, a cover 60 is slid to cover the image forming opticalsystem 41, the finder optical system 43 and the flash lamp 46 with thecover 60. Moreover, when the cover 60 is opened to set the camera 40 toa photographing state, the image forming optical system 41 is broughtinto a non-collapsed state a shown in FIGS. 37 and 39. When the shutterrelease button 45 disposed in the upper portion of the camera 40 ispressed, the photographing is performed through the image formingoptical system 41 in conjunction with the pressing of the button. As theimage forming optical system, any of Examples 1 to 18 of the presentinvention may be used. In this embodiment, the zoom optical system ofExample 1 is used. Therefore, the image forming optical system 41comprises the first lens unit G1, the second lens Unit G2, the thirdlens unit G3 and the fourth lens unit G4. The aperture stop S isdisposed in the second lens unit G2. An image of an object is formed bythe image forming optical system 41 on the light receiving surface of aCCD image sensor 49 via the low pass filter F coated with an IR(infrared) cut coating and cover glass. The image of the object receivedby the CCD image sensor 49 is displayed as an electronic image in theliquid crystal display monitor 47 disposed in a rear surface of thecamera via processing means 51. This processing means 51 is connected torecording means 52, and the electronic image can be recorded. It is tobe noted that this recording means 52 may be disposed separately fromthe processing means 51, or may be constituted so that the image iselectronically recorded in and reproduced from a storage medium such asa hard disc, a memory card, a DVD±R, a DVD±RW or the like. The cameramay be constituted as a silver salt camera in which a silver salt filmis disposed instead of the CCD image sensor 49.

Furthermore, the objective optical system 53 for the finder is disposedalong the finder optical path 44. The objective optical system 53 forthe finder includes a plurality of lens units (three units in thisexample) and two prisms. These optical elements constitute a zoomoptical system whose focal length changes in conjunction with the zoomoptical system of the image forming optical system 41. The object imageformed by the objective optical system 53 for the finder is formed onthe view field frame 57 of the erecting prism 55 which is an imageerecting member. Behind the erecting prism 55, there is disposed aneyepiece optical system 59 which guides an erected image into anobserver's eyeball E. It is to be noted that a cover member 50 isdisposed on the exit side of the eyepiece optical system 59.

The digital camera 40 constituted in this manner is small in size andhas an excellent performance since the image forming optical system 41has a high performance, is small-sized, and can be collapsed whenstored.

Next, FIGS. 40 to 42 show a personal computer as an example of theinformation processing apparatus in which the zoom optical system of thepresent invention is built as an image forming optical system. FIG. 40is a front perspective view of a personal computer 300 whose cover isopened, FIG. 41 is a sectional view of the image pickup unit 303 of thepersonal computer 300, and FIG. 42 is a side view showing the state ofFIG. 40. As shown in FIGS. 40 to 42, the personal computer 300 includes:a keyboard 301 for inputting information from the outside by anoperator; information processing means or recording means (not shown); amonitor 302 which displays information to the operator; and an imagepickup unit 303. Here, the monitor 302 may be a transmission type liquidcrystal display element which illuminates the rear surface with backlight (not shown), a reflective liquid crystal display element whichreflects light from a front surface to display the image, a CRT displayor the like. In the drawing, the image pickup unit 303 is built in anupper right portion of the monitor 302, but this place is not limited,and the system may be built in any portion around the monitor 302 or thekeyboard 301.

The image pickup unit 303 has an image forming optical system 112including the zoom optical system (not shown) of the present invention,and an image sensor chip 162 which receives the image formed by theimage forming optical system 112. These components are built in thepersonal computer 300.

Here, the optical low pass filter F is additionally attached onto theimage sensor chip 162, and integrally formed as an image sensor unit160. The image sensor unit can be fitted into a rear end of a lensbarrel 113 of the image forming optical system 112 by a one-touchoperation. Therefore, the image forming optical system 112 or the imagesensor chip 162 need not to be made alignment adjustment or surfacespace adjustment. Therefore, the image pickup unit can easily beassembled. A front end of the lens barrel 113 is provided with coverglass 114 for protecting the image forming optical system 112. It is tobe noted that a driving mechanism of the zoom optical system in the lensbarrel 113 is omitted from the drawing.

The object image received by the image sensor chip 162 is input intoprocessing means of the personal computer 300 via a terminal 166, anddisplayed as an electronic image in the monitor 302. FIG. 40 shows, asone example, an image 305 photographed by the operator. The image 305may be displayed in a communication partner's personal computer in aremote area via processing means and the internet or the phone.

Next, a cellular phone convenient to carry will be described as anexample of the information processing apparatus in which the zoomoptical system of the present invention is built as an image formingoptical system with reference to FIGS. 43 to 45. FIG. 43 is a front viewof a cellular phone 400, FIG. 44 is a side view of the cellular phone,and FIG. 45 is a sectional view of the image forming optical system 405.As shown in FIGS. 43 to 45, the cellular phone 400 has: a microphone 401which inputs operator's voice as information; a speaker 402 whichoutputs talking partner's voice; an input keys 403 by which the operatorinputs information; a monitor 404 which displays the operator, aphotographed image of a talking partner or the like and information suchas a phone number; a image pickup unit 405; an antenna 406 whichtransmits and receives a communication radio wave; and processing means(not shown) which processes image information, communicationinformation, input signal and the like. Here, the monitor 404 is aliquid crystal display element. The arrangement of the constituentelements is not limited to that shown in the drawings. This image pickupunit 405 includes: the image forming optical system 412 disposed alongan image taking optical path 407 and including the zoom optical system(not shown) of the present invention, and the image sensor chip 462which receives the object image. These components are built in thecellular phone 400.

Here, the optical low pass filter F is additionally attached onto theimage sensor chip 462, and integrally formed as the image sensor unit460. The image sensor unit 460 can be fitted into a rear end of the lensbarrel 413 of the image forming optical system 412 by the one-touchoperation. Therefore, the image forming optical system 412 or the imagesensor chip 462 does not be made alignment adjustment or surface spaceadjustment. Therefore, the system can easily be assembled. The front endof the lens barrel 413 is provided with the cover glass 414 forprotecting the image forming optical system 412. It is to be noted thatthe driving mechanism of the zoom optical system in the lens barrel 413is omitted from the drawing.

The object image received by the image sensor chip 462 is input intoprocessing means (not shown) via the terminal 466, and displayed as theelectronic image in both or either of the monitor 404 and acommunication partner's monitor. In a case where the image istransmitted to the communication partner, processing means includes asignal processing function of converting information of the object imagereceived by the image sensor chip 462 into a transmittable signal.

It is to be noted that when the filter such as a low pass filter isomitted in each embodiment, the camera can be constituted to be thinwhen collapsed.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention. Rather, the scopeof the invention shall be defined as set forth in the following claimsand their legal equivalents. All such modifications as would be obviousto one skilled in the art are intended to be included within the scopeof the following claims.

1. A zoom optical system comprising, in order from an object side: afirst lens unit having a negative refractive power; a second lens unithaving a positive refractive power; a third lens unit having a positiverefractive power; and a fourth lens unit, the zoom optical systemchanging a space between the lens units to thereby perform zooming andfocusing, the fourth lens unit being fixed to an image surface, thefirst lens unit comprising a biconcave negative lens, the zoom opticalsystem satisfying the following condition:−3.0<(r _(1GF) +r _(1GR))/(r _(1GF) −r _(1GR))<0.3 wherein r_(1GF)denotes a paraxial radius of curvature of an object-side surface of thenegative lens of the first lens unit, and r_(1GR) denotes a paraxialradius of curvature of an image-side surface of the negative lens of thefirst lens unit, and wherein the total number of lenses included in thezoom optical system is six.
 2. The zoom optical system according toclaim 1, wherein each of the first lens unit and the fourth lens unitincludes one lens element.
 3. The zoom optical system according to claim1, wherein the third lens unit includes one lens element.
 4. The zoomoptical system according to claim 1, wherein the fourth lens unit has apositive refractive power.
 5. The zoom optical system according to claim1, further satisfying the following condition:0.6<TLG _(sum) /f _(W<)1.7 wherein TLG_(sum) denotes a sum ofthicknesses of the lens units constituting the zoom optical system, andf_(W) denotes a focal length of the zoom optical system in thewide-angle end.
 6. The zoom optical system according to claim 1, furthersatisfying the following condition:0.2<TLG _(sum) /f _(t)<1.5 wherein TLG_(sum) denotes a sum ofthicknesses of the lens units constituting the zoom optical system, andf_(t) denotes a focal length of the zoom optical system in a telephotoend.
 7. The zoom optical system according to claim 1, further satisfyingthe following condition:−3.0<Δ_(12WT) /f _(W)<−1 wherein Δ_(12WT) denotes a difference of aspace between the first lens unit and the second lens unit in thetelephoto from that in the wide-angle end, and f_(W) denotes a focallength of the zoom optical system in the wide-angle end.
 8. The zoomoptical system according to claim 1, further satisfying the followingcondition:−0.9<Δ_(12WT) /f _(t)<−0.3 wherein Δ_(12WT) denotes a difference of aspace between the first lens units and the second lens units in thetelephoto end from that in the wide-angle end, and f_(t) denotes a focallength of the zoom optical system in the telephoto end.
 9. An imagetaking apparatus comprising: the zoom optical system according to claim1; and an image sensor disposed on an image-surface side of the zoomoptical system.